I speak from experience here

A Cir Pac CAN BE CONVERTED to DONE3 or above, and can even be converted back down to a Cir Pac

Have done this before, and when their is an upsell there was no penalty, but if moving down from a DONE4 (which almost all RTW fares will be more than Cir Pac's) to a DCIR22 or DCIR26 the cancellation fee of 10% was applied

All RTW's are refundable less a penalty prior to departure, despite what the endorsement says

The next post I add on this subject of RTW's will blow you away

Stay tuned