1) The contract itself can't be edited, of course, but the Witch would be more than willing to renegotiate the means for your character's stay. So basically, yes, that's fine.

2) When he regains his Winged Kuriboh card, he'll still be able to interact with it as in canon. However, it'd only be visible to others (non-canonmates) if they were appropriately spiritually sensitive.

I hope that answers your questions! Please ask if you'd like any clarifications.