Multi-Cam : how to assign a different multi cam to an existing sequence

So, I have a unique question, like I seen to have often.

Here is the situation. We have a sequence that is set to 2.7K anamorphic. So is the multi-cam attached to it. For reason I won't go into, we need to change the settings of the sequence AND the multi-cam sequence, WITHOUT impacting the already existing sequence AKA non-destructive workflow.

Therefore, I made a copy of the sequence, changed its settings  to 4K 16x9 aspect ratio / non anamoprhic.

Because I don't want to destruct the original sequence in 2.7K, I wanted to make a copy of the multi-cam sequence and change the settings of that one to 4K 16x9 / non anamorphic and re-scale the footage.

BUT I don't know how to re-assign or replace the multi-cam sequence associated to the sequence in order to rescale the footage to fit the 4K 16x9  sequence. If I do change the settings of the multi-cam sequence from 2.7K anamorphic to 4K non-anamorphic and rescale the footage, then it will impact my 2.7 K anamorphic sequence. 

For some reason, I really have a hard time to explain this, but I hope one reader will make sense. If not, please ask me further questions.

Thank you~