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Some songs should not be covered by Blood, Sweat, and Tears... or, like, anybody, most likely.*
Quick flow chart: Was it played by James Taylor?
Yes: No. Don't make a Blood, Sweat, and Tears cover of it. Just don't.
No, but Chicago played it: It's probably ok. They're like almost the same thing, only Chicago is poppier, while Blood, Sweat, and tears is sort of hippie-ish. And Chicago does nothing but sentimental love songs just about, which kind of makes them suck.
No, other: Maybe, but think long and hard about it first.
The end.
* - ok, so it's never really possible to close the window on the possibility totally, but some songs have versions so definitive that you'd better know what the fuck you're doing before you try to reinvent it or whatever.