It's possible that a scope or open sight adjustment will get you back on track with the heavier bullet. The biggest obstacle holding you back isn;'t the added bullet weight - but the diffferences in plastic sabots/bullet diameter.

You may be better-off to switch to another 40/50 bullet. My 40/50 195 gr. Barnes Expanders would shoot the same as my T/C 200 gr. Shockwaves. So when all else fails, try another 40/50 bullet around 200 grains.... or switch to loose powder - for easier load-tweaking than with pellets.