Hi,
do I need to remove the headliner competely in my 85 ta t-top, to replace the front seatbelts?

 

it's possible to do it just removing the rear plastic (between the headliner and the hatch), the black plastic inside the doors that support the headliner and the sail panels but be very careful its easy to break the headliner that way. It can be very flimsy and break in half or you could just break the corners apart while working on getting those bolts out from the seat belt retractor. It is possible just be very careful if you go that route.

 

Considering the headliner is 24 years old if it still original, I would just take my time and remove it. Chances are it will break when you bend it to remove the belts. If in fact it is original, you might want to remove it anyway and see if it needs any strenthening or possibly a recover.