Play it by ear. If it means your gonna sererely cut into reps you could skip the towel on shrugs and maybe after your workout do a dead hang from a chin-bar with towel. On the ohter hand it will strengthen your grip very quickly so that can only help you.
If your grip is shot for shrugs but you're wanting to do the wrist curls you could try Hise shrugs using a calf-raise machine or even a barbell. That way your grip won't be involved at all. But it's not gonna matter much in the long run
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