Gentlemen. There is a difference between logging PIC and being PIC.

An appropriately licensed and rated FO may log PIC time on his/her legs.

For many 121 major and national carriers this would be the kiss of death during an interview.

For many 91 and 135 operators this would be acceptable and help you meet insurance minimums.

My advice is to not log it until you are in the left seat. If you do decide to log it; create a separate column to track 121PIC for when you have upgraded.

Some employers will immediately show you the door for logging PIC while assigned as an FO.

Why risk it.