after going through several Mac tech folks who claimed the drive was soldered to the motherboard and not replaceable, I spoke with an Apple senior manager yesterday who said that mid-2015 MacBook Pro’s would automatically void their warrantees if the 256 ssd was upgraded to a 512 Mac ssd. she said that their might be some special exception that a Mac authorized repair center might be able to get. it all appears to be intentionally clouded in mystery, and I wasted gas going to two Best Buys yesterday before I discovered this all. Microcenter seemed willing to do it, but apparently according to Apple, it's not as simple as that (Microcenter was also saying the upgraded SSD card was over $1100 for 512 and $1300 for 1 TB. this was the final answer:
Thank you for contacting Apple. It was my pleasure to assist in your question resolution. Should you need further assistance on this issue in the next 30 days, my contact information is listed below.
I am enclosing a copy of the limited warranty for you. Please discuss the option to replace your hard disk with the AASP, and ask them to get approval through their Apple channels before making your final decision:
Apple One (1) Year Limited Warranty (https://store.apple.com/Catalog/US/Image...)
If Apple approves the upgrade without touch your warranty, then it is fine, but the hard disk itself should be a replaceable part, as was your initial question.
If I am not available, please feel free to call 1-800-275-2273 and ask for Senior Advisor support to continue troubleshooting.
You can also connect to our online 24/7 Chat support at Contact Apple Support (http://getsupport.apple.com).
Thank you for using AppleCare.
Teresa- T2 Mac AppleCare Advisor
Phone: 1-877-203-0418 Ext. 1163240
or Email: email@example.com (mailto:firstname.lastname@example.org)
Schedule: Thursday- Monday 11:00am-3:00pm EST then 7:00pm- 11:00pm EST
(If responding to my email, please click the email listed in my contact info above)