Went tripping down the Rabbit Hole on the question of cutting the cap tube, Parker says "wont work" (in another thread)

Thats a refrigerant cross-charge head and apparently always has vapour phase which would be lost.

Next point of disorder, changing the thermostat assembly without recovery.

General concensus is "cant do it without refrigerant loss" which is true, as it has no isolation valves.

so, how about 'minimise vapour loss over the 15-20 seconds needed to swap the head?"

Trane XL14C heat pump. Externally equalized TXV via a long cap tube.

According to Sporlans data, that external TXV has no pressure commuted to the bottom of the thermostat disc from the input or output lines (sealed), only the Eq cap tube, which is a long, small restriction which is only seeing vapour-phase.

This change could be done at night when the outdoor temps are ~ 60F. The indoor coil cover must be removed to access the TXV, which also exposes the indoor coil to cool air. The inlet (cold air return in the dwelling) can be blocked, windows opened and indoor fan run to draw outdoor air thru the indoor coil to cool the sealed system down to outside ambient, which will reduce the system pressure from ~230 psi down to about 170. That would means much less vapour loss.

???????

PS it is VERY easy to stop a Trane.