QTR-Quadtone RIP

I printed my first tablet, contact printed it, and while I was checking the results, I noticed that the gray percentages in the Photoshop file were off. I opened the original file (the step tablet used by Ron Reeder) which has a Gray Gamma 1.8 profile attached (I guess this was done as a workaround to print without Color Management but now with Print Tool is not necessary any longer).

I had converted (not assigned) the color profile of this file to Gray Gamma 2.2 and this changed the gray percentages.
I am not very familiar with Gray Gamma but I always though that the profile conversion should not change the values in the file.

So my question is: can I just assign Gray Gamma 2.2 to this file?
I tried and it did not change the gray percentages, but I am not sure if something else, less evident, will come up later on.
Thanks,
Luciano

OK, done some more research and it seems that I should really use assign if I do not want to change the values of the steps, but I would be grateful if someone with more experience chimes in
These are the two articles I found:
http://www.dpug.org/forums/f8/qtr-changing-embedded-profile-step-wedge-2150/
http://www.largeformatphotography.info/forum/showthread.php?79565-Convert-Gamma-1-8-to-2-2
Thanks,
Luciano