Can you convert from a total submusclar breast implant to a partial submusclar with local anesthesia and sedation?

Dear munirah97x,
it is hard to tell for sure without an examination. If you are considering surgery, I would suggest you consult a board-certified plastic surgeon. Only after a thorough examination, you will get more information and recommendations.
Daniel Barrett, MDCertified, American Board of Plastic SurgeryMember, American Society of Plastic SurgeryMember, American Society of Aesthetic Plastic Surgery

First, implant revision surgery under local would be challenging because the local anesthetic would have to be injected close to the implant and risk puncture.
Second, you should be aware that dual plane involves detaching a portion of the pectoral muscle which can cause animation deformity. Another option is split muscle, which maintains upper pole coverage but leaves the muscle attached.

Augmentations are not totally under the muscle, but changing to a dual plane cannot be done under local anesthesia. You may not notice any difference in shape. If you want more fullness, go with a taller implant. If you want less fullness, go with a flatter implant. Fat can be added if needed under general or local anesthesia.