From what I can research on my own, during the tail end of the Qing dynasty ie sometimes before the Xinhai revolution of 1911, wearing a modern short hair is basically an open declaration of a revolutionary. Earlier still, students of various modernizing movements studying abroads would also cut their braid. Also, some Chinese living in territory ceded to foreign power can also wear modern hairstyle eariler still. But those are all modern hairstyles, not the pre-Qing traditional ones.
In Qing controlled territory, of course, exemptions and special cases still exist. For example, Taoist monk would continue to wear Han traditional long hair. And certainly many outlaws throughout the dynasty wear traditional hair as a symbol of their defiance.
But what if I am from a somewhat respectable family living in a big city still under control of the Qing dynasty, thus neither a Taoist monk nor an outlaw? What if I just really like the aesthetic of the hairstyle? Would I get into any trouble beyond being stared at by my neighbors if I actually gone through with it?
The Qing queue edict was not simply a means of designating those who might be politically untrustworthy; violation of it was a capital crime. If you grew your forehead hair out except for a handful of special dispensations such as being in mourning, then you were publicly declaring yourself an enemy of the state and would be executed with little fanfare. The reason outlaws had no problem growing out their hair was, well, in the name – these were people living outside the law, aware of the consequences of being caught. I discuss the queue edict at greater length in these two past posts:
As I allude in those posts, the 1860s would, frankly, have been an especially bad time to suddenly develop a predilection for Han hairstyles given that several rebellions – many still in progress – had broken out whose participants signified their allegiance by their defiance of the queue edict. Chief among these were the Taiping, whose association with this was so strong they were known to their enemies as changmao 長毛 – literally, the 'Long Hairs'. Having the wrong hairstyle in the wrong place would literally get you killed; when travelling from one area of control to the other it was often necessary to shave to enter Qing territory – and often to have to spend time tanning to mask the obvious tanline from having shaved too recently – or to spend time growing one's hair out to enter Taiping lands. Making the wrong choice about one's hair at the wrong time was fatal. Moreover, for the purposes of our hypothetical 1860s nativist, the Qing sometimes offered cash bounties for severed rebel heads, with the size of the bounty scaling with the length of the forehead hair (5 inches being the maximum). If you, a Han man in a Qing-held city in 1860s China, chose to grow your hair out, you were going to die.