apope,
You could, in theory and of course practice, convert phones from Digital to IP [52xx/53xx] on an offline DB, but then you would have to reload that DB back into the MiVO-250; which causes it to reset.
When you convert a Digital to IP on an offline DB it will close the DB programming down on you so when you start it back up you will need to do so from the last occurrence and not from where you save it at. This means that it will ask you if you want to save the session for future use you would have to click the Save button or you will lose the conversion you just made.
This is probably not something you are aware of if you didn't know about the ~ for Directory names which is why I brought it up. It would be best to get your vendor to show you how to do it properly so you don't mess anything up; which you can.
This most likely is not something you would be doing during business hours of course, but it sounds as though you are not a vendor and could possibly make use of this for the one off scenario.
This would keep all of the programming intact for that user and then all you would need to do it change the Keymap on the phone to the new IP Keymap.
Of course the 52xx/53xx series IP Phones have already been discontinued so you can't get those new anyway and if you are converting to 69xx series phones then this process wouldn't work for you.
Your vendor should have already made you aware of this, but the ability to buy new licensing for this particular system is running out soon and you may not be able to get licensing to convert from Digital to IP in the near future. If I were you I would get the licensing now or think about how you are going to approach a system change out in the future.
It is sad to see this little system go away as I don't think there is anything on the market today that can do what it can for the target audience it was meant for.
Thanks,
TE