If all your dps macros are like:

/cast [target=focustarget] Shadow Bolt;

then you can just leave the target open for use as focus in the older macros.

Check it:

#show Seduction
/assist [target=target,noexists]; [target=target,dead] focus
/petstay
/petfollow
/stopcasting
/cast [pet:succubus,target=target,exists,harm] Seduction; Seduction


Should work, I'll go test it now.