Sorry I updated to the latest MCC version. This is a bit absurd. Looks like only alpha and digits are allowed in a Template name.
When *exporting* a Template to a file system, cleaning up the name (based on the needs of the system) may be needed. But the template in the MCC software should support the characters of the current (or a recent) Unicode standard.
In the interest of greater inclusion, the software community expended significant effort to expand the domain of standard expressible characters to 149,186 (as of Unicode 15).
I'm guessing that this restriction of the latest MCC was a knee-jerk reaction to some special situation ("Quick - patch it before it goes out!"), but this is overkill.
Interestingly, when you import a memory from the device, the auto-assigned name has all kind of punctuation. And when you [Save As], the generated name has an underscore.
Please reverse course on this one ...