Unfortunately there seems to be a growing trend among GMRS groups that modified ham gear are magically OK for use on GMRS frequencies. The leaders of one GMRS group in my state have been pushing the Icom IC-2730 as the radio to get for GMRS. To suggest to them that it isn't acceptable only gets you laughed at and told that the FCC doesn't care and that we shouldn't either. Whether it works or not or whether the FCC will come fine them or not isn't the key factor; it's still not an accepted radio for GMRS according to the rules.
I've run into similar things at work a few times.
Someone needs radios. Instead of asking the department that handles radios, they talk to their friend, random people on the internet, or "fly-by-nite communications inc." and buy a bunch of CCR's.
When they don't work right, they complain to me. I point out the problems with the low quality equipment, lack of type certification, licensing issues, various other FCC violations. In return I get "Well, the guy on the internet said it was OK and the FCC doesn't care".
Unfortunately, the internet has made everyone an 'expert'. There are far too many radio 'experts' out there that don't understand what they are doing and cover it up with "The FCC doesn't care.".
In other words, self proclaimed experts with zero professionalism, zero attention to detail, minimal skill.
Back to what was asked, I'm also not aware of a 'grandfather' rule that somehow makes radios type accepted for GMRS when they never were.
Because there isn't. Type acceptance is required on FRS, GMRS, MURS, etc. There is no grandfathered clause that permits the use of hacked amateur radios. And the FCC -does- care.