I know this app, Photo Editor, much better than Picsart.
exactly right. i never install picsart, photowonder,.... these apps always run in backrgound and access my galery without my knowledge.
i don't think kingroot or any one click root can help, these apps will easily brick your phone.
XDA forums will give you detailed instruction to root your device.
as i know, you can mod app and make some adjustment on theme, text, icon.... if you can but i don't know if it is illegal or not (Android is an open source platform?)