Historicly yes.
Hood, wing and gondola had some adjustment. Motor cannon were locked inline with the airscrew shaft and the gunsight was adjusted.
In our game the motor cannon tilt up to the white hood MG line and slide up/out along that from 150-650. The Ta152 is the only motor cannon that apperes to be locked into the motor line while the green 20mm line slides angled up to it 150-650.
If you set your K4 30mm to 200 it will average a flat kind of shot to about 400 becasue of the slight loft in the uptilted barrel. Fly the K4 at 290 true airspeed auto leveled against the the target and shoot at full zoom 200, 300 and 400. The dispersion pattern and slow velocity is your bigger problem. Not the drop when you set it's convergence to 200.
I beleive it's the green gun line for most of our aircraft in the game that your gunsight is zeroed to when you change convergence. The closest you will get to changing the vertical is to create gunsights where you place the reticle center higher or lower in the bitmap mask. But, then thats a bit of the reason some gunsights had tick marks below the center mark aside from bombing and rockets.
I think the center line of sight for the gunsight mirrors the green gun line sliding down the white hood MG line or an invisible line for wing only guns. It's the only way I can account for your gunsight center being zeroed at any convergence point you pick.
Is it realistic?
Test it this way.
Set a 190D9 20mm to 275. Fly against the offline target and auto level at 280 true airspeed. Shoot at 275, 400 and 550 while on full zoom. Do your rounds zero at 275, shoot high at 400 and pattern center at 550? Yes it would be nice once you pull your convergence out to 275 that you can lock your gunsight center and 20mm elevation there. Then angle out your 20mm to cross at 550.
Try a P51D convergence 300, auto level 285 true. Shoot at 300, 500 and 800.
In the game consider how often you really kill any cons past 200-300 in a fighter. The verticle componet is slightly irrelevent becasue the game models your nose dipping when you fire wing guns. Check the La's when you fire their guns against the offline target. Your nose raises. Motor mounted gun fighters stay steady becasue the recoil is inside of the engine line. I've failed to test what gondolas do to 109's though.