Can these be used on completed fuel tanks? If not, how can I get fuel caps to replace the ones that came in 2017 as part of the RV-10 wing kit?

All fuel tanks (excluding RV-12 legacy) shipped since late 2017 to early 2018 now use the T-00007 type fuel cap and flange. Earlier kits shipped with the T-406 cap and flange. These are not interchangeable. The hole diameter for the original T-406 in the tank skin is 2.343 where the T-00007 cap is 2.625.