I'm almost done with replacing my head gasket; I have the timing set, the engine mount is back on, and the intake manifold is back on, but I decided to do a cheap leak down test by blowing compressed air into each cylinder and putting a piece of paper over the adjacent cylinders to determine if there's any head gasket leakage. Turns out there is a little bit of leakage between 3 and 4. I think this is because a couple of head bolts were popping a bit when I installed them so I think the head bolts need to be re-torqued (correct me if I'm wrong but I think I can re-use the new head gasket since it's layered metal). So can I retorque the head now as is or do I have to take the timing belt off to relieve that tension on the head?

Retorque them, it's not going to be putting that much tension on it

Leave timing belt on.

Specs don't call for retorque so if you correctly tightened and torqued the head bolts to spec that should have been the end of it. (unless you forgot to remove all the liquid that was sitting in the head bolt holes, before installing the head bolts)
I personally would redo the head bolts---complete redo of only ONE at a time though. Remove the bolt, extract any liquid from the bottom of the threads if necessary, relube bolt including the washer, and retorque. Then redo another bolt. (9 tight bolts are gonna keep that head gasket squashed, I'd expect no issues)

Before you sweat it, see if your air movement was simply because several valves were open during your check
If the engine was set on #1 tdc that's the only cylinder with all the valves closed. If you apply air to any other cylinder that air may escape through open valves. Gotta roll it over for each cylinder/piston individual tdc before putting air pressure on that cylinder.

make sure valves are actually adjusted correctly
beware that removing the head and setting it down flat can bend all the valves that were open at the time, and there are always some valves open .

I am curious how this may have worked out if you are still on this forum?