How much would the Greenland landmass isostatic rebound contribute to long term climate change?
Be warned this is a general (and speculative) answer, but it was getting too long to be a comment: The bulk of Greenland's ice mass is centred over inland/central Greenland. If you were to take all the ice away today, much of central Greenland would actually be below sea level, by several hundred metres in fact:



Glacial isostatic rebound would seek to equilibrate the loss in mass by 'popping' Greenland back up, but it appears that we'd be starting from at or below sea level over much of the island! I'm afraid I don't have any figures to hand over what the total isostatic adjustment might be in the centre, but I would be skeptical of it producing peaks any higher than the current ice sheet level - so the net effect on atmospheric circulation in this region may be small.

Interestingly, the post-glacial isostatic adjustment going on in that region is not as simple as may be expected, some areas over Greenland are actually still sinking, due in part to the movement of former ice mass from the Arctic into the seas around Greenland (as water). The figure below indicates that the areas to watch are actually Canada and Scandinavia, at least for now.


For the existing tall peaks that are rebounding, in general terms you could potentially expect more orographic precipitation enhancement as they became higher, more erosion, which could lead to greater drawdown of CO2 from weathering...the arm-waving speculation goes on... (but see this question.)

From a regional climate aspect, I would perhaps be more concerned over the decrease in albedo on Greenland from the loss of its ice cap. Also, the potential effect of changing surface moisture fluxes to the atmosphere, should central Greenland end up becoming a series of lakes and islands (rather like Finland in its post-glacial state today).