Back Lever (basics)

I'm very close to a back lever with a chin-up grip (can do it with pull-up grip), but have decided to do a massive de-load and progress slowly all over again towards the full hold later on in the year, to prevent any injuries etc.

Last week I started with the tuck all over again.

Question: I tried contracting my triceps during the hold, almost in a way that exaggerates a straight arm locked position. It made the strain on my biceps tendon and forearms greater (but in a way that felt good). Is that a good idea? I'm trying to emphasise an exaggerated straight arm position, because when I see gymnasts do straight arm skills, their arms look almost hyper-extended!

No, it's a bad idea. There's already enough stress on your biceps from gravity without having to work against your triceps at the same time. You shouldn't have to actively flex the triceps to achieve a straight-arm position. There is no reason to seek hyperextension of the elbow: athletes who perform strength skills that way simply have elbows that naturally extend to that position.