Making Units retrainable but not trainable?

[Steward Denethor II]

I think I read somewhere on these forums that it is possible to make a unit retrainable but not trainable with certain buildings. How would one do this, if it is possible?

Example: Having Knights of Santiago still require the Santiago guild to build but making them able to be retrained at a citadel. This is only an example BTW.

[PapaRosario]

Set max pool to any value under 1. For example, you can set it to 0.99. That way, the unit can be retrained even if it is depleted 99%, but a full unit can never be trained.

[Steward Denethor II]

Wow super quick reply, Thank you!