You have 1282 memorized transactions? Hit the edit button on one.

On edit the only thing I see that references to using a template is in 'Action' > Template Only. Is that what I need?

That list of 1282 records ARE your templates.

right, i see now. so do you where on these templates we could update the tax code?

You edit the transaction that's the template to update the tax code, and then rememorize it.

Ah right - so it's the transaction that needs updating and then remomorised, delete old ones.