Hi,
I *think* you have two issues here and they are getting confused
A/ You already run 4.7.3 running under PHP 5.?.? which is working fine
B/ You want to upgrade to 4.7.6 running under PHP 5.?.? which I do not see a problem doing
C/ The only time you will have an issue is when you "switch" to PHP 7
Now the un-encrypted files will be needed
BUT they have not been updated (I don't think?) to work with PHP 7.
You now need to work out what is not working (Deprecated) in the un-encrypted files for the mod. You will be able to make the changes to the files as they are open.
I *think* that is were we are?
Hope that helps to clear the way?
Kind regards
ITVV