You can use Tankerman-PIC to work on barges. As others have noted, if you have the time and transfers on tank ships, why not get the (tankship) Tankerman-PIC? This way you have it, but if you take Tankerman-PIC (Barge) now and later decide you’d like tankerman-PIC, you won’t have the recency and may not be able to get it.
The difference between the two is the cargo course (4 days for barghe vs. 5 days for PIC) and the fire fighting course. The Basic Fire Fighting that is good for a license and for STCW BST is good for all tankerman endorsements, the tankerman barge course is the same length of time (2 days) but uses less equipment, so it is not acceptable for a license or STCW.