Active and pending membership issues

Ok, I'm hoping someone has dealt with this issue before and can help a girl out. We did a step up donation this year asking donors to give a gift to FY18, FY19 and FY20. People did and everyone was happy, except me because the memberships weren't allocated correctly and all the gifts for future fiscal years went into the FY18 memberships. Now I'm faced with moving a few hundred memberships around. One of the problems I'm running into is adding an active and a pending membership at the same time through Tessitura. I can deactivate the FY18 (now that our FY is over) and add the FY19, but can't add a pending FY20. I've also been fixing these through sql one at a time and it's tedious, so my question is twofold.

1. Can some explain to me how I can enter a pending membership for a gift that we've already received?(I tried to do an adjustment through a batch, no go)

2. Has anyone done this and developed a bit of code that might help me move this project along a little faster and save some of my sanity?

I'll take any and all advice!

Thanks,
Melissa