Command & Conquer Remastered Collection includes the source code for both C&C and C&C: Red Alert, which means modders should be able to totally overhaul both games. That's wonderful, but for simpler tweaks, one of my favorite things about the original Red Alert still works in the remastered version: You can replace all of the default world, building, and unit variables with a magical little file called rules.ini. Want your rifle soldiers to shoot Tesla coil zaps? Just change one line, and voilà.
Rules.ini is not included when you download Command & Conquer Remastered Edition from Steam. Luckily, Red Alert Archive still hosts the original rules.ini file from back in the '90s. You can download it there, or you can copy the contents of the file here, paste them into a new text file, and then rename it 'rules.ini' (make sure your folder view settings are set to display file extensions).
However you grab it, once you've got rules.ini, drop it into your Command & Conquer Remastered Collection install folder. On Steam, you can find that folder by right clicking the game in your library, navigating to 'manage,' and then selecting 'browse local files.' It's called 'CnCRemastered.'
As long as rules.ini is in that folder, any changes you make to it will override Red Alert's default variables. (Note that rules.ini will only affect C&C: Red Alert, and the original Command & Conquer doesn't have an equivalent.)
All that's left is to edit it. If you don't have a program set to open .ini files, tell Windows to use Notepad or WordPad—it's just a text file. The list of variables is pretty straightforward and well-commented, although it can take some trial-and-error to get the effects you want. To give basic infantry Tesla guns, you'd find 'rifle soldier' under 'infantry types,' and change the 'Primary' variable to 'TeslaZap.' Now rifle soldiers shoot electricity, as they should.
For some reason, editing the attack dog entry doesn't work. I seem to remember having difficulty with that back in the day, too (maybe try editing the 'dog bite' attack instead). Otherwise, I've tested a few other variables and my changes showed up in the game as expected.
You won't be able to make complex total conversions just by dicking around with an ini file, but you can do quite a lot with it. I remember creating air units that could only attack other air units, because I was really interested in WW2 dogfighting back when Red Alert came out (I was also 11). I also recall making a special rules.ini file for purely air and naval wars, probably designed to go along with a long lost collection of custom maps.
All this simple variable modding was a big part of my experience with Red Alert as a kid, and so I'm pleased that the detail wasn't overlooked in the remaster (or, at least, wasn't removed). I've only spent an hour playing around with it, but so far the Remastered Collection has ticked all the 'aw, they actually care' boxes I could want. For instance, I was delighted that a redone version of the Red Alert installer greeted me the first time I launched it. Remember when installers were part of a game's world? And as Wes said, the music alone is a treasure.
