If you wanna do it, here's how.
First, download this image: https://static.wikia.nocookie.net/logopedia/images/d/da/ROBLOX-Circle-Logo.png/revision/latest?cb=20141109070109
It's a WEBP file, so then go to https://cloudconvert.com/webp-to-ico to convert it to an icon file. (download it)
Now go to the Roblox Player and select properties in the right-click menu.
Click "change icon" and find the new (or actually old) icon file in your downloads.
Click on this file then press "ok".
When back to the properties menu, press "Apply".
Roblox should now have the classic low resolution icon.