could you extend the belt throughput quality change to loaders? specifically modded loaders :3

Loaders should already be affected by the "belt changes" option.

local categories = {"transport-belt", "splitter", "lane-splitter", "loader", "loader-1x1"}

Undergrounds are also affected (different part of the code, since it's possible to only modify underground length while keeping belt speed constant).

The only "belty" thing that isn't affected are linked-belts, since these need to be connected to each other via script, which might cause compatibility issues.