No, the parts are not interchangeable. Ballpoint and rollerball within a Meisterstück line may look very much alike, but they are fundamentally different inside. The rollerball is a pen with a screw-on cap that seats on a thread on the section. A twist ballpoint has no such cap at all: the upper part belongs to the body and carries no cap thread, and to change the refill the body is unscrewed in the middle.
The impression that both pens can be “unscrewed” is therefore misleading — these are quite different threaded joints with quite different workings behind them. Anyone looking to replace a lost or damaged cap on a rollerball will get nowhere except with the cap of an identical rollerball from the same line and finish, not with parts from the ballpoint.