Given a situation like this, I'd find the CG with the tank full, 1/2 full. and empty.
There will be a spread. Then, I'd compare that to any +/- tolerance given for the model.
If the 1/2 tank fell within the tolerances, I'd try it!
One afternoon not too long ago, I was flying an Advance 25 (electric power)
All of a sudden, it started acting quite squirrelly.
When It was safely back on the ground in one piece, I quickly discovered that the 4S 3300mah battery had been sliding back and forth
almost 1/2 the length of the battery. While the plane was still flyable, elevator trim was way off, and I think that the battery must have slid
at least partway back forward during the landing approach.