Enter GREP. You can enter in a fairly simple GREP query that will find all Arabic numerals with a single hyphen and change those hyphens to en dashes. Try this one next time you have to update your hypens to en dashes:

Choose Edit>Find/Change
Click the GREP tab
Add the following strings:
Find What: (?x)\b(\d+)-(\d+)\b
Change to: $1~=$2