Is there any way that an irish Free State could've been etsablished before 1900, whether by diplomacy or force of arms ? What'd be the best POD for such a scenario to arise ?
Not really. It took the introduction of Conscription to create enough desire for independence to actually fight over it, and a war that took large numbers of Loyalist Catholics away to die in a far off field.
It depends on what is meant by the Irish Free State. There are two possibilities one being that the 1798 uprising succeeeds which relies on the French making a successful landing and Wolf Tone recieving support. This one is probably unlikely. The other scenario lies with Gladstone successfully delivering home rule and avoiding the disastrous split in the Liberal Party. Possibly he offers Chamberlain a programme of social reform. The Liberal Party stays in power and introduces measures such as payment for M.Ps thus retaining the support of trade union leaders. Home rule may be a halfway house to greater powers including dominion status particularly if there is a radical liberal government in power. There may have been an Ulster problem and there may have been an opt out for parts of Northern Ireland which would make it even more like the free state
The Fenians would be isolated as they were anyway and as the wise men have told us their cause was a failure