Selling Lots and SMA (Special Memorandum Account)

My broker allows me to sell shares in the lots that they were bought.

For example, the fictitious NuCo, In., in order of purchase:

Lot A: 300 Shares of NUCO at $20
Lot B: 300 Shares of NUCO at $17
Lot C: 600 Shares of NUCO at $12
Lot D: 600 Shares of NUCO at $15

Let’s say Lots A and B were bought using leverage and all others were bought with cash. I was able to buy A and B by borrowing because the majority of the account value sat in long term positions that that allowed A and B to be purchased well below to margin limit.

If want to sell lots C and D at $16, will I have paid my broker back, or still be using the borrowed margin account money?

The default sell order is FIFO (first in, first out).

This is a simplified version of a bad position I bought my self out of. The numbers were made up in order to show an average cost-per-share around $15.

I would like to sell off C and D to take the earnings and hold A and B expecting a recovery.

Since A and B were bought on margin, would they remain loans if I sold C and D.