Cannot edit signature on outlook 365 mail

I am not sure if this has solved the problem only for me or whether this solution is translatable to everyone else having this issue.  

I too was having the issue where I had 5-6 signatures in outlook, all of which were useable, but only one of which was editable via any of the methods people are recommending.  I reviewed several similar threads and was not able to find a solution.

It occurred to me that the signatures must be stored somewhere and I have at times edited or deleted my Outlook templates by locating them in Windows Explorer so I decided to try something similar.  It may be that this solution only works if you are using the Outlook Desktop Application.

What I found is that signatures are stored in the following location:

C:\Users\Username\AppData\Roaming\Microsoft\Signatures

Where "Username" must be replaced by your Windows username

When I navigated to this location, I noticed that each signature has a folder and three files associated with it. 

I discovered that the signature of mine which was usable and editable had a different file naming convention than the rest of my signatures.  Specifically, all of the files had my email account in the filename as shown below:

In this image, the "03 Limit Raised" signature was visible and editable in Outlook and the "02 Approved" signature was not.  You can see that the signature that was working has my email account in the file names.

NOW...there is a shortcut here.  If you are simply looking to delete old signatures, deleting the relevant files and folders in this location will do that.

From there, the simplest way to edit old signatures is to open the Word document corresponding to the signature you want to edit and copy the contents to use as the basis for a new signature you will create.  The new signature you create will use the new file naming convention and will be both usable and editable.  You can then delete the old files and folders in the location above to remove these from the list of available signatures.

OR if you like doing things the hard way like me, you can rename all of the files and folders in the folder shown above to match the new naming convention.  The only slight trick to this is that within the folder for the signature you are trying to edit, there is an xml file (Filelist.xml) that directs outlook to the files in this folder The naming convention in that file has to be updated as well (that file can be opened and updated using notepad.  If successful, all signatures will be visible and editable after outlook is restarted.

I realize that this is a back-end workaround, not a straightforward front-end solution, but it worked for me.  Hope it helps someone.