ILIAS Developers: manipulating html of page content

hello together,

we restrict HTML for the page editor in our instance.
for one use-case we need now HTML.
our idea was to create a plugin which prepend the needed structure/html to the page.
we tried around with ilUIHookPluginGUI and getHTML(). but with that we could only manipulate the right column.
(also it seems this is deprecated cause of global screen extension?)

how (without creating as "page object/ilPageComponentPluginGUI") can i manipulate the inner html to add there some special html for a specific ref_id?
(#ilContentContainer .il_center_col)

thanks a lot!