Your understanding is outdated. The FCC clarified the vagueness in their rules that many interpreted to mean that a Part 90 commercial radio could be legally used on the GMRS frequencies back in 2017. Here's the current rule regarding what equipment can be used on the GMRS frequencies (
click here to go to the source FCC web page:
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Subpart E of Part 95 is the GMRS rules. What that means is your radio needs a certification to Part 95E in order for you to meet FCC regulations for use on GMRS frequencies. If you are using a commercial (business) radio for GMRS, in addition to its Part 90 certification, it would need a Part 95E certification. Those are rare.
That said, I wouldn't worry about using your radio for GMRS. Just be aware that it is not legal. As long as you are not being stupid, the FCC has bigger fish to fry. From an ethical standpoint (if that's more important to you than the legal standpoint), the airwaves are public, so as long as you're not impacting other users of the airwaves anymore than you would be with a legal radio, you can sleep well at night, if that's important to you. Part 90 radios are very well made, so the chances of inadvertent interference with other users is minimal. Now, cheap Chinese radios are another story altogether. I've heard rumors that some of the early Baofeng units would walk over other frequencies, and that's a bit rude.