Functionally, can a sway brace be replaced by a variable spring hanger, placed horizontally?

No because a variablespring hanger does not work horizontally, it must work vertically.

Variable Spring and Cro-Moly 3-bolt Clamp Assemblies for a Power Generation Facility
Variable Spring and Cro-Moly 3-bolt Clamp Assemblies for a Power Generation Facility
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