You can use a regular expression in the find (or in RegEx Pal) to make the change from . to :
In the find you must start with regex:
Here is one possible search:
regex:(?<=\\fr \d+)\.(?=\d)
This says, do a regular expression search for a period preceded by \fr and one or more digits, and followed by a digit.
The replace string would be just the colon.
If you wanted to find any period preceded by a digits and followed by a digit you could remove the \\fr