Replace Thumbnails and Theme Switching ♦

[Advice Request]


I am currently making an extension, and I hope I could get some
practical advice on feasibility :

I want my extension to go fetch/load a local folder of custom homescreen
thumbnails(top-sites), and then replace the auto-generated thumbnails in
the homescreen with those it loaded.
The extension would be able to read the associated domain names of the
thumbnails and then replace them accordingly (e.g :
Pinned Url : : Ok so it’s YouTube : then
replace the thumbnail with “Custom_Youtube_Thumbnail.png”)

Does that seems possible to you ? (Before I dive in head first)
I saw that the top-sites API is not quite available but maybe I’m wrong.

Extra : My extension is switching themes (like this : ).
Would it be possible to switch the thumbnails accordingly
(Custom_Youtube_Thumbnail_light.png > Custom_Youtube_Thumbnail_dark.png)
as i’ve made a version for each.

Would be a pleasure to hear your opinion on this, or just pointing
useful resources to me,
I’m not asking for a perfectly baked solution.
Hope I’ve been concise.
Thanks for reading me !

[End of Advice Request]