Will,
If open the table, select a record in the field you wish to change [ID], click on Replace, in the Home Tab - Find.

Fill in the following details:
Find What: -
Replace With:    [Leave Blank]
Look In: Current Field
Match: Any Part of Field
Search: All

Click Replace All

Now change the Data type to Number and in the format add "#-#".
Change the number of #'s depending on how you wish it to be formatted.
12-34 = ##-##
If you want it as a number you can't have a - in it but you can display it using the formatting above.
This will make all the IDs display with the same formatting.

Alex