Hey peterws, hope I understand what you mean.
if you select the piano you like,
then freeze parameters (maybe don't freeze string length but set it manually for the right piano after the procedure below, if you want),
then select a new piano, click on for example a Steinway (the chosen parameters will be applied),
then save that altered piano now with a name you choose like "My Steinway BL 01" (remembering to manully make the strings the right length, or not).
For future clarity about what you did, you can also click "edit" text that shows up when you select your piano - make notes in there like "my BL settings, via freeze function - string length manually kept at ..." that kind of thing.
That might help if you find that you'd like to do more editing later, for example if you find you need to alter lots of little things per piano to make the frozen params 'work' better via a few tweaks, you can note those there so you know where you left off - just number your versions 01 02 or a and b etc. Consider you might also want to delete any you have improved and no longer need to see cluttering up your folder. And/or better,
To make it easy to open and play, just save out all your new BL custom pianos into their own folder, labelled something like "My BL pianos". That way, you just click your folder, click the piano at top of interface and you see your custom pianos, none of the defaults or any other stuff in the way.
May seem a hassle, but sincerely, for each piano you'd like to do this, it may take less than a few minutes - or a few minutes in total, for an easily managed go-to library of your own making
Pianoteq Studio Bundle (Pro plus all instruments) - Kawai MP11 digital piano - Yamaha HS8 monitors