1: Home Rule kept Ireland within the Empire while historically, Ireland wanted Independence
Home Rule was a stepping stone in the Home Rule Bill of 1914 which for it to be enacted required that: (a) The Great War to come to an end (b) Both pro-union and nationalist parties in Ireland enter into a dialogue that would lead to a mutually acceptable compromise.
As there was no such compromise reached it was proposed under the Government of Ireland Act 1920 that Ireland be temporarily partitioned with each entity being given Home Rule - again this stage was seen as a stepping stone towards unification and independence.
2: it was signed on the basis that Ireland would be partitioned temporarily, but was made invalid, even to its loyal Irish supporters, by Britain secretly altering it to permanent partition.
First of all from what has been written no-one can have any idea what the IT was that was supposed to have been signed, but by process of elimination the only thing that could have been signed by any Irish delegation would be the Anglo-Irish Treaty (6th December 1921) Neither the Home Rule Bill 1914 or the Government of Ireland Act of 1920 which were Westminster Bills would be signed by anybody other than the King when giving it Royal Assent.
No "secret alterations" were made to either:
(a) Third Home Rule Act 1914 (b) Government of Ireland Act 1920 (c) Anglo-Irish Treaty 1921
So as far as "secret alterations" go Jim Carroll is havering. None of the above had any reference to anything other than temporary partition in (a) and (b) above. The Anglo-Irish Treaty Articles contained an article that provided Northern Ireland with the facility to opt out of any independent Ireland and remain as part of the United Kingdom. That article was on the table from the start.
3: Britain tore up the signed agreement and replaced it with one bulldozed through by the Northern Unionists.
Britain tore up NOTHING
Anybody wishing to check the accuracy of what I have written above please consult the online texts of:
Home Rule Act 1914 Government of Ireland Act 1920 Anglo-Irish Treaty 1921