So, what you are licensed for is a narrow band FM repeater.
Often (not always) you can get approved to change emission designators if your new emission is completely within the envelope of the original. What you won't be able to do is change to something like trunking that doesn't get along well with other users on the same frequencies.
Really, the only way to know for sure is to ask. Whoever did your licensing should be able to help you. As was stated, you do need to get the license changed to match what you plan on using.
Personally, unless you really need the functions that digital provide, I'd stay with analog. The equipment will be cheaper.