AI, which is not guaranteed 100% accurate, suggests...
"To create and save a custom 12/8 time signature in NCH Crescendo:
Right-click on an existing time signature or an empty area of the staff where you want to set the time signature.
Select "Time Signature" and then "Number" or a similar option to manually enter the time signature numbers.
Enter 12 as the upper number and 8 as the lower number to set a 12/8 time signature.
This manual entry allows you to use 12/8 even though it might not be listed as a preset.
To save this setting, save your composition as usual through the "Save" or "Save As" menu. Crescendo automatically saves all score settings, including custom time signatures, as part of the file.
This way, each time you open the saved composition file, your custom 12/8 time signature will be preserved and ready for use."