Can a repository package be upgraded from outside the repository?

[Jim Byrnes]

When I did a fresh install of 14.04 I choose to install jEdit 5.1 from 
the repository. I am not ready to upgrade to 16.04 yet but I see it has 
jEdit 5.3 available. I checked and there doesn't seem to be any backports.

I the past I have installed jEdit by adding dl.sourceforge to my sources 
list and using apt.  So if I did that now would my present install of 
5.1 be upgraded to 5.3?

I don't want to uninstall 5.1 and then install 5.3 because of a lot of 
customization I have done to 5.1.

Regards,  Jim