[Before creating a patch/copy/taking over abandoned addons]
If you want to take-over an abandoned addon/Before creating a patch/copy of addons
Read the addon's comments if someone else of the community has posted a fix or a fixed version or another replacement for download, and use this instead
If not: Try to contact the author of the addon via private message, the addon's comment section or if a github link is given via the github repository -> bug report/feature request
Maybe yu will find the dev at the esoui addon dev chat
If you personally want to take over the addon: Having multiple patches and versions of the same addon is just confusing the users and often creates new errors as ppl install several versions at the same time and files/folder will get corrupted via Minion e.g. So at best do not create a copy but maintain the original addon. If the old addon dev in charge gave you the approval you can be added to the team of the addon and keep on maintaining it.
Ask the admins of www.esoui.com (Dolby, Cairenn) via private message then to add you to the team and forward them the info of that other dev in charge.
Do not create any copy and silently work on it, before having read the addon's licensing info first!
Licensing is no fun and you can get into severe trouble, if you do not respect them. They are written laws and need to be followed as this.
If the license tells you you are NOT allowed to copy or alter the code etc. Accept it and do not try to find a workaround.
Plagiarism also involves intellectual crimes!
Maybe ask the dev of the addon if he will add you to the team as described above.
If the license tells you you are allowed to use the code, follow the licensing rules (and include the license in your fork/copy if the license tells you to do so) if you plan to create a fork/copy fo the addon. ALWAYS give proper credit to the addon(s) and developer(s) you have used as a base (even if it was only a mental/intellectual base, or you only had spyed the code to learn from, but have not included it 1:1. Give credit and be fair!).