Is there any way to overwrite some files in extension webjars without directly modified the .jar in data/extension/repository subfolders?
eg. I would like to modify some codes in \META-INF\resources\webjars\application-ckeditor-plugins\1.15\xwiki-upload\plugin.js for my site. Is there any way (like placing the modified plugin.js to some folder or edit some XWiki page?
Overriding just one file is doable for JAR located in WEB-INF/lib (trough WEB-INF/classes) but I don’t see much way for installed extensions.
The clean way in your case is to create a new CKEditor plugin starting from the code of ‘xwiki-upload’ plugin, see http://extensions.xwiki.org/xwiki/bin/view/Extension/CKEditor+Integration#HUseadditionalCKEditorplugins . Then you can disable the standard ‘xwiki-upload’ plugin from the Administration and load your own plugin instead.
Hope this helps,
Marius