Changing filenames with wildcards

[stupomer]

Having trouble with this

In a folder there are two files

one with an extension (.oly) and the identical one without, e.g.

\101 Week 24 T2
\101 Week 24 T2.oly

The 101 part is variable so let's say it's

C:\*24 T2
C:\*24 T2.oly

I want to add the extension .ches to the ones without an extension

I have tried

Code:

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ren* "C:\*24*air" "C:\*24*air.ches"

but it doesn't like the syntax
also I tried getting string of filepath, getting its length and adding the .ches as a string using the insert command

but it doesn't seem to like * in the syntax

Additional questions:

is it possible to use Regex expressions in filepath names

is there a way to append to the end of a string without knowing it's length ahead of time?

Thanks,
Stuart