Well if thats the only concern of you then I can tell you that 2DA merging is not required at all, its recommended to do but not vital for anything, if you want I can help you integrating any CP version into your module/PW, send me a message.
As far as poison related, my new poison "engine" allows several things that would help you to make basically anything you want.
My new poison system allows to apply custom poison without any effects except effect you will code in script. Retaining the poison icon and green hitpoint bar (or not if you dont like). And it assign the effects of the poison to the newly constructed object which acts as an effect creator so all poison effects can be identified in other scripts like Neutralize Poison spell, so even if you make a poison that apply, Idontknow paralysis, the new Neutralize Poison spell in CP will automatically cure it. The DC is still problem however that can be workarounded with new custom poisons in poison.2da where you can code a "generic poison" with rising DC, that is 10 for first line, 11 for second. (Hmm neat idea, will probably do for CP 1.72 myself)