I'm no expert on this but I can say this:

I had a chase UA Visa for just shy of a year. I cancelled it but first I asked them to move its now freed up credit line to my remaining Chase CO MC. They did this.

Then I applied for another chase card and when it was first denied, I called in and ask them to simply borrow credit from the CO MC so I could get this new card, and that way they weren't putting themselves out.

Well, I got double lucky because they were about to do just that but then they ended up giving me the new card AND more credit.

Point is, either way, do try to move the existing available credit line you have been granted to something else CHASE and THEN cancel.