How "fungible" are memory maker fabs for switching between memory types?

[Xebec]

How easy is it for Samsung, SK Hynix, Micron, etc. to switch production between memory types -- examples: DDR5 to GDDR7, or DDR5 to HBM.

I suspect the DDR5 to GDDR7 example is pretty quick - with downtime measured in hours or low days, and is similar to say TSMC changing production between different logic chips.

I imagine that DDR to HBM is significantly harder because of HBM requiring stacking where DDR is not stacked today, though perhaps it's not too bad if the 3D stacking is ~heavily decoupled from the memory production lines.

I just want to learn a bit more about how quickly (or not) the various memory makers can pivot between ("popular") RAM technologies.

Thanks!