Modifying CARB compliant Honda gas caps (extended run system

Has anyone modified the CARB compliant Honda gas caps when making an extended run fuel system? I have the large diameter caps that click when they're fully tightened on the generator. The CARB compliant caps are two piece and rattle when the generators are running, I would like to modify those caps and keep the new (old style) caps that I ordered from Amazon when I use the gens without the extended run tank. Will the CARB caps be airtight after the modification assuming I do a good job of installing the gas fitting and sealing it with JB weld?