You cannot choose which one you want to bill based on reimbursement - you have to follow the policy. The blepharoplasty is considered incidental to the ptosis repair, so you would just bill the 67904 unless the blepharoplasty was performed on the opposite side, as described below, which would justify adding a modifier to unbundle it.
The Medicare guidance for this is located in the NCCI Policy Manual, Chapter 8, Section D, paragraph 12:
CMS payment policy does not allow separate payment for a medically necessary blepharoptosis procedure (CPT codes 67901-67908) and medically necessary blepharoplasty procedure (CPT codes 15822, 15823) on an ipsilateral upper eyelid. NCCI contains PTP edits that bundle blepharoplasty procedure CPT codes 15822-15823 into blepharoptosis procedure CPT codes 67901-67908. A physician may bypass these edits with an NCCI PTP-associated modifier if the blepharoptosis procedure and the blepharoplasty procedure are performed on contralateral upper eyelids or with appropriate modifiers in accordance with Medicare policy if the blepharoplasty procedure is a cosmetic procedure. If a medically necessary blepharoptosis procedure and cosmetic blepharoplasty procedure are performed on an ipsilateral upper eyelid, the cosmetic blepharoplasty may be reported but is not a Medicare covered benefit.