Would this program work the other way as well, if I replaced the contents of the folder "newBMPs" with the old files?
Also it would be cool if it took some parameters, like a source folder from which to take files and a target file to which to pack the new files.

Awesome, thank you.

Attached it to the first post.

it's an update to the exe found in the larger archive, if memory serves.

Not sure how v2 does the job better but for me it returns error:
Error: Expected hi-res3Dss.exe resfile bmpfolder
Example: hi-res3DSS.exe backup_1\CITMAT.RES newBMPsPress any key to continue . . .

v1 seems to be okay though...

Any particular reason why one should opt for v2?

I hope I'm not necroing this topic by asking, but do you guys think any of the textures would look better if re-upscaled with xBRZ instead?

Theoretically, most textures should look way better when upscaled with something that is not HQx since it is a rather basic filter. I did some testing with a Fringe pattern and some basic textures (why Minecraft? Simply because did not have the original SS textures at hand). For the sake of it, I also tried waifu2x and Smilla Enlarger, both of which I have personally used before. W2X is meant for mostly flat textures like cartoons, or in fact anime, and uses some sort of Deep Convolutional Neural Networks magic, whereas Smilla was developed for photography. I'd say a mixture of xBRZ and W2X might be best, the latter seems to have a surprising amount of problems with single-pixel, non-45° lines, but the results for voluminous textures are way less artificial than xBRZ. But feel free to interpret the results yourselves.

I've been trying to get the V2 version to work but no matter what I do (I assume I have to copy/replace the files identical to the V1 ?) it says it doesnt find the folder.
V1 .bat file works but when I put the citmat.res file back into the game, textures of 3D objects appears corrupted.
Is it possible that you release a V3 standalone version that works with SSEE ? now that we can play the game in 4K this mod makes much more sense

I've had a little time to experiment.
Turns out, HackEd was (almost) capable of doing that, all that's missing was an importer for .bmp files.

See attachments to this post:
First, a source port compatible mod (the archive). Contained README.txt describes how to install.
Second, pictures show a selection of 3D Objects, both with and without the mod enabled (seems like the low-res screenshots are ordered first, see filename on mouse-over to be sure).

If you are happy with it, I'd go and publish it then on moddb (hence the timeout of the attachments).

Re extra folder: The readme does mention the step of creating a folder. If I add the folder to the archive, then the readme isn't immediately available, as it is moved as well. I'm torn about this and opted for the current variant.
Which case is more likely?
* People "know" how mods work, ignore readme, and complain they have to create a folder
* People don't know how mods work, would want a readme front and center
* People don't know how mods work, ignore readme, and... know how to complain?
* ...
I guess a combined variant is the compromise: put readme and the mod-folder into root of archive.

The readme also specifies the package being version 3.0, as it's a new packaging, and specific for the source port. Also to separate it from the previous two versions.

(Plus: Did you choose .7z to keep up the mixture of compression formats like in the first post? 7zip is not universally installed, .zip is supported natively in MS Windows)

I'm also considering to name it "HighRes_Object_Textures_..." as (possibly) someone wants to make a mod for actual high-poly-count objects - which is also why it's registering itself that way in the game.

Will update all of that later today - tomorrow morning latest.

ah, those are the ones from 3rdPlayer.
So, I'm the heretic then (female hacker also had everything in the root dir). All good.