Long version:
In late 1796, with the blessing of the rebel United Irishmen, the First French Republic launched a failed invasion of Ireland (Expédition d'Irlande), under General Hoche.
The Irish strategy was to remove the British from Ireland and declare a Republic, with the aid of the French. The French sought to deal an ideological blow against the British, and establish a potential base for an invasion of Britain.
It seemed like a mutually beneficial strategy at the time, and I can see how the United Irishmen's Fitzgerald, O'Connor, and Wolfe Tone were encouraged by the promise of French military aid, but I have often wondered whether it would have simply been a case of "out of the frying pan and into the fire". By which I mean, would Ireland have simply changed hands from what was essentially a British colony to a French colony, leaving the population in a similar position to its original predicament.
In other words, how detailed was the agreement between the Irish and the French; was it perhaps shrouded in a fog of mutual idealism?Is there any evidence that the French had plans other than those outlined to the Irish?
In short, my answer would be no. That's not to say that there wasn't a history of this, as with the sœurs républiques, but 1796 under Hoche was only the first attempted expedition, with a further two later on, and Ireland was a very strategic path to access Britain. Each time, their presence had been effectively requested as aid, and they worked in coordination with Tone et al. By 1798, Napoleon and the Directory were prioritising Egypt in both numbers and attention, with Humbert's force arriving too late to help the Rebellion. I don't think these details correspond to aggressive policies of annexation.
Military history and particularly the expeditions outside the métropole are definitely not my area, but I think the bulk of scholarship on Ireland and France during the Revolutionary years has been produced by anglophone rather than French historians. I'm only vaguely familiar with Elliott's 1982 Partners in Revolution, for instance, and that's about it for Ireland. But I had a look for you at the Serna/Francesco/Miller edited volume (2013) on Republics at War, and Sylvie Kleinman's chapter ('Tone and the French Expeditions to Ireland) deals perfectly with this in line with my initial thoughts. She quotes an extract from a Directory letter to Hoche (p. 83):
The Irish, like every nation in the world, have a sort of religious respect for certain emblems and principally those that led their ancestors into battle. It is possible to turn this respect and attachment for their ancient emblems to the advantage of the revolution which is being prepared in their country [...] It will not be unprofitable to embark some musicians destined to carry to Ireland the tunes of liberty which have stirred French republicans in battle.
This revolutionary evangelism is nothing new, and certainly doesn’t equate to ambitions of annexation. As the Directory wrote to Hoche (cited by Kleinman again, p. 91):
The aim, citizen-general, is to restore to a generous people ripe for revolution the independence and liberty they clamour for. Ireland has been suffering for several centuries under the odious yoke of England. The arrival […] of assistance from the French Republic can only be the signal […] of a general insurrection.
It was, then, a convenient strategy that conformed perfectly with the Republic’s liberating ideals, lambasting England’s oppression and tying their revolutionary values in with more direct military interests:
[…] By detaching Ireland, England will be reduced to a second-rate power.
I’d take a look at her chapter, as she goes on to describe "Directorial policy on postinvasion occupation and governance" through Tone’s diary, according to which, in their discussions, Hoche had Tone make explicit his intended form of government (p. 92):
Hoche repeatedly asked about the type of government the Irish wanted: France’s ‘main object was the independence of Ireland, under any form of government’, though it would prefer a republic. Tone confirmed […] it was ‘most undoubtedly a republic’.
Eventually, however, as Kleinman points out:
[…] the vexed question was posed: If the insurgents did not assemble, the Irish forces in British pay did not dissolve, and London sent substantial reinforcements, was the country to be treated ‘comme une conquête?’ [… But:] A final version hastily drawn up by Tone […] clearly reiterated that the French came ‘to emancipate, not to conquer your country’, and would ‘respect property, persons and religious practice’.
Still, it appears more a pragmatic attempt to cover all hypotheticals as necessary, rather than revealing of underlying annexational desires, indeed raised by Hoche to ensure that the French would be acting as much as possible in hand with the Irish in case of unforeseen circumstances.
Generally, the French Republic was busy trying to survive and most important to survival was fighting the enemy abroad. Due to the politics of the French Directory (which were corrupt), the Directors were interested in keeping the war abroad and keep people busy in order to ensure that they do not push against the Directory, so the Directory pushed military campaigns outside of France and "export" the Revolution. It was successful in Italy with Napoleon but failed to be effective in Germany and Spain. The Irish campaign isn't so much a move of help to Ireland but rather a way to try to cause problems for the British.
So, it really isn't something about doing something good for Ireland or creating a French colony (colonies weren't something that the Directory was interested in) and just to mess with the British in order for them to divert resources away from the Coalition.