Full Flash Locked T43 TCM

Tried to read the (what I thought was stock) TCM on my T43 in a 2016 Chevy Colorado Duramax. Ran into an error when trying to read the file and talked to my new tuner. They told me I’d have to re-link to the previous tuner’s FlashScan, then have the previous tuner send me a stock/unlocked TCM file and then Full Flash the TCM.
My question is, can’t I just Full Flash the TCM with the new tune file and also have the new tuner send me an unlocked factory TCM file just in case I need to go back to stock? My understanding of the Auto-Lock Calibration feature is that it prevents the tunes from be read from the module. But one still can full flash over an existing tune on the module. Is this correct?

Ask your previous tuner to unlock your TCM, he may want to flash it back to stock.