I think there is to much for that to work !!! Maybe you could minimize the loss.
Anyway if you need to change the fluid for a better one, ie better shifting, now the time !!!
( MT90 from Redline is generally recommended here)
GA is about 3.5 quarts, SR about 4 quarts.
Well if its got royal purple in it then I am not surprised you want to only top it up.
I got about a quart when i pulled my driver side axle, and i think i deliberately tilled it, measured it and replaced with new through the front fill hole.
I didn't take the speed sensor out, i knew the fluid was close enough to being correct as i drained and refilled with MT90 when i did the clutch.