In order to reproduce the bug: [1] Create a new template folder in the Template Manager. [2] Select the new folder and try to rename it. I did not found a possibility to do this. Neither there is a symbol in the icon bar, nor there is a context menu, nor F2 works in order to rename the template.
ok :)
With default settings for template paths, create a new "folder" in the Template Manager and save a template to it. Then go back to the Template Manager, click on the name of the "folder". Now you are in edit mode and you can change the name. There is no need for a context menu or special key, you can simple edit the name as you would edit other fields. The name changes are registered in the file groupuinames.xml; it does not change any folder name on disk. But the situation is not as easy. In Tools > Options > LibreOffice > Path you can add other paths to the item "Templates". And only one of them can be marked as "the default path for new files." In former versions of the Template Manager it was actually about the properties "read-only" and "writable" and in this meaning it is still used in the renaming feature. So when you now try to edit the "folder" name in case the "folder" belongs to a path which is not the default path and therefore handled as being read-only, then you cannot edit it. So there are three issues here. (1) The UI gives no message, why renaming is not possible. (2) The meaning was changed from "writable" to "default", but the feature 'renaming' has not been adapted. (3) The UI gives no hint, that renaming is possible. I write "folder" because it is not really a folder in the sense of the OS file management, but it can contain template files with total different paths.
Fixed with https://cgit.freedesktop.org/libreoffice/core/commit/?id=37b4163ce16a6171bd25653494e58bc03daedc2b
Checked with version 5.2.1. In the new template manager folders are no longer used. Instead categories are used. These can be renamed. Hence bug closed.