I have a Rear 7 speed 11-30 Shimano cassette. I'm about to change it and notice it's labeled "Interactive" on the cassette locking ring. The crankset is a 3-ring and it says "use IG chain only". However I replaced it with generic 6/7/8 chain and it seems to work and shift great.

Can I replace the rear sprocket to a Hyperglide etc? Do I have to stick with IG components only?

What year and hub is it? If it uses a lockring chances are you should be able to fit a hg cassette.

ItsI a Raleigh c-200 I believe based on the serial number it's 1998 or 97.

I have removed the cassette it uses a standard threaded ring with a Shimano spline.

You have answered your own question i think.
One spline wider than the rest?
Is there any marking on yhe cassette?
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Get the same num of speeds as before.
Chain lenght may or may not need changing.

The only issue I ever had with using HG chain on an original IG-equipped bike was a tendency for the chain to derail itself off of the big ring toward the inside, down to the middle ring.
This wasn't an adjustment issue, and I fixed it with some subtle modifications to the IG big ring's teeth, and which solved the problem for me.

The problem tended to occur as the chain was shifted toward the larger cogs, something that the original all-IG setup tolerated gracefully.

I noticed the text "For use with IG chain only" on a tiny label on the large chainring.

IG chain is still available.