Your question makes the assumption that a) both these icons were created during the American Revolution, and b) they were intended to glamorize the snake itself, rather than the symbolism behind it, and c) it makes the assumption that calling someone a snake was in the common vernacular at this time. None of these two are in fact true (at least not entirely true for part a and there is no evidence to support an alternate position on part c).
The 'Join or Die' image that appear in many high school textbooks actually predate the American Revolution by over 20 years. Originally appearing in Ben Franklin's Philadelphia Gazette, this image was created to promote the idea of unity in May, 1754 during the beginning of the French and Indian War. The French and Indian war was becoming a global affair, soon after killing thousands and causing all sorts of hardships across Great Britain's colonies -- especially those in North America. Financial stresses and watching military aged men go off to fight in the Colonial militias deeply divided the colonists. Many wanted to abstain from war. They saw it as something that they didn't want to be a part of. Worse, is that blame began to be pointed between different colonies, since some, like Virginia, were thought to have instigated the start of the war. And that's where Franklin's cartoon came in. Appearing alongside his essay which focused on the "dis-united states" of the colonies, Franklin warned of the dangers of refusing to unite for a common cause. As one historian put it, "It appeared first in the Pennsylvania Gazette May 9, 1754, just a month before the Albany Conference was called to form a union of the northern colonies against the Indians."[1] This was a pivotal moment in colonial history as Franklin warned:
The Confidence of the French in this Undertaking seems well-grounded on the present disunited State of the British Colonies, and the extreme Difficulty of bringing so many different Governments and Assemblies to agree in any speedy and effectual Measures for our common defense and Security; while our Enemies have the very great Advantage of being under one Direction, with one Council, and one Purse.
It's simple from Franklin's perspective. Great Britain didn't intend to fully support the war with its own Army. Instead, they expected to Colonies to handle the fight in North American mostly by themselves. But unlike France, the colonies were disjoined -- almost like separate countries -- which made everything a challenge in assembling a unified defense. That's why he made this cartoon. The "Join, or Die" is saying that if all the colonies don't join together, they will die separate deaths.
The actual drawing of the severed snake was also pretty symbolic on different levels. Old wives tales in Colonial America believed that a severed snake could rejoin with its missing parts or regenerate those missing pieces [2]. So Franklin was pretty much saying, if the states unite they can ensure their survival, and if not, France was likely to win. It was a powerful statement that resonated deeply with these colonists. The image was a hit, and was reprinted in newspapers across many states in the weeks and months that followed.[3] Skip ahead a few decades, and the same images and themes became resurrected when fighting Great Britain's policies led us on our path to war. The snake, already deeply imbedded in the minds of the American colonists as a symbol of unity, was brought back to remind the colonists of both the power of unity, and the consequences of standing alone. So the symbol was not intended to glamorize the snake, but rather play into the old wives tales that everyone knew in an attempt to foster unity. It would be adopted by the colonies during the prelude to the American War for Independence, particularly in Boston.
Similarly, the Gadsden Flag (don't tread on me) depicts another snake. This one was created during the first year of the American Revolution in 1775 by Christopher Gadsden. It is likely that Gadsden took inspiration from Ben Franklin who, in 1775, wrote under a pseudonym to propose that the rattlesnake was perhaps an appropriate symbol to represent America.
She may therefore be esteemed an emblem of vigilance.—She never begins an attack, nor, when once engaged, ever surrenders: She is therefore an emblem of magnanimity and true courage.—As if anxious to prevent all pretensions of quarreling with her, the weapons with which nature has furnished her, she conceals in the roof of her mouth, so that, to those who are unacquainted with her, she appears to be a most defenseless animal; and even when those weapons are shown and extended for her defense, they appear weak and contemptible; but their wounds however small, are decisive and fatal:—Conscious of this, she never wounds till she has generously given notice, even to her enemy, and cautioned him against the danger of stepping on her.—Was I wrong, Sir, in thinking this a strong picture of the temper and conduct of America?
Gadsden used his new flag initially as his personal guidon on his naval ships, but it wasn't until 1778 that it was adopted formally by congress. I think that popular TV shows/movies have made it seem that this flag was waving by popular crowds in the early 1770s, which it most certainly was not.
So to answer your question as best I can, if the term "you're a snake" was negative during this period, I can't comment on whether or not it was temporarily relieved of usage during the period. What we do know is that the symbol of the snake was embraced from the French and Indian War and onwards and that it continued to evolve as a symbol amongst some Americans during the war.
I hope his answers your question even though it's not as direct as I wish I could have made it. Please let me know if you have any follow ups.
Kirkland, Frederick "An Unknown Franklin Cartoon". The Pennsylvania Magazine of History and Biography, Vol. 73, No. 1 (Jan., 1949) [pp 76-79]
Cook, Karen. "Ben Franklin and the Snake that Would Not Die." The British Library Journal, Vol. 22, No. 1, IMAGES AND ICONS OF THE NEW WORLD: ESSAYS ON AMERICAN CARTOGRAPHY (SPRING 1996), pp. 88- 111. http://www.bl.uk/eblj/1996articles/pdf/article5.pdf [pp 95]
3. Kirkland, Frederick. [pp 76]