New player here. I like and plan to learn lot of Eagles, Earth Wind & Fire, Fleetwood Mac, 70's classic rock and the like. They all tend to have what I consider a full, round, warm bass tone to them, maybe what people refer to as dark? I know T. Schmidt uses Jazz bass for the most part. J McVie has used J and P basses.
GAS has hit a bit and already have 2 basses; 1980 T-40 & 2009 Ibanez SR500.
I am hoping to get one of them to sound similar to the above artists and others of that era. I know I should just get a J, JP or P bass, but I have what I have for now.
The SR500 is pretty modern and aggressive sounding to my ear and should be a great fit for my other taste in hard rock/metal genres. It has a nice hard hitting sound to it as is. It has round wounds that are in good shape and good sound so I want to leave it alone.
The T-40 however is supposed to be the chameleon of basses and it has visibly worn flatwounds that need to be replaced. So I was thinking of changing strings to help it fill the classic rock niche. I am wondering what strings folks would recommend to help take some of the highs out and warm up the sound a bit. I was thinking tape wounds maybe? I have ready they are warmer/darker, last a long time and lighter tension might also help me play longer with my untrained fingers?
I wouldn't worry about matching all of the different basses which your favorites play, an impossible quest normally. I do not own one, but from what I have seen & heard, the T-40 is a
very versatile (if heavy) bass, between that bass & your amp EQ you will have
a lot of possibilities.
If you like the flats which are currently installed, you can take a picture of the strings at the head stock and at the bridge (also include a shot of the ball ends) and people here may be able to help you identify them. Even if you do not like them, you could do the above and describe what you don't like & want more or less of (tone wise & feel wise) compared to
those strings, and people can then assist you in the direction you want to go.
As others above have said, wipe down & keep the old strings if you do replace them, they may be OK (flats can last 8 years to infinity

... if they intonate correctly, are not dead as a door nail, and get the sound you want, keep them on), someday you may want to try them again & be glad you did.
I agree with
@4StringDave, for the players/timelines you have mentioned, the Fender 9050L flats are a good place to start. If you EQ accordingly, they can even do the Rotosound 77 thang and with a foam mute get thummpy. They are neither pure old school thumpy nor "modern" close to round wounds. Middle of the road. They are very affordable, well made (designed by a TB member here) and unless you EQ them out, as 4StringDave mentioned, have strong mids, which can help sit/cut in a band rock mix when needed. With the possibilities of your T-40 & your amp EQ, you should have a
very wide range on tones to choose from with them.
Should you find them too old school or too modern (do give them a couple of months though, they take a bit to break in), well, then you will know in which direction you need to look/head for with the next set of stings.
Fwiw, I like rounds and flats, (so a 50% weirdo according to some posts above

), unless you are indoctrinated into one single genre (which you apparently are not

), having both can be very useful.
- Henry