Xposed is a search term that will bring you up results for things such as framework modules and codes, APK developers, and system behavior for lollipop and marshmallow. Get ready to have some fun and type in the word Xposed. If you took my advice and are continuing along now, you see a page in front of you that reads Xposed module repository. If you have created a module or have permission to use another module and would like to upload it to this site, this is the place to do so. It will, however, have to be free because there is no paywall on this site.
Utilizing modified APKs there is no true way to combine them that is unless of course the creator has multiple APKs that have various combinations. Utilizing Xposed you can manipulate framework modules and alter the system behavior without actually having to touch your APKs. This allows for certain modules to be able to effectively work alongside different versions, sometimes it even works alongside different ROMS and will not have any changes occur.
Having access to a place to post your modules allows for a multitude of different applications and potentials. Xposed is part of a Drupal open source community. If you are looking to contact Xposed module repository you can do so from their websites home page. You will see a contact link in the top right-hand corner. Here they clearly specified that there is no support for Xposed framework and no support for any modules that will be found by this link.
The only known issues with the APK are boot loops when using Samsung stock ROMs, a fatal signal 6 is known to cause ROMs to boot loop, and there are a few other minor issues. All of these can be tweaked out through the discussion forum where there are threads along with attached files for APK and ZIP files for both installs and uninstallers for Xposed .