Is it safe to wear magnetic bracelets after heart bypass?

Yes. It should be okay for the vast majority of patients. Few patients have had CABG with distal and proximal anastomotic magnetic connectors and I am not sure if a magnetic bracelet will have any influence.
No effect on bypass. Coronary artery bypass surgery attaches a separate blood vessel to the blocked coronary artery, at a point beyond the blockage, to resume blood flow to the the heart muscle. Magnetic bracelets should not affect bypass surgery. If there is not an electrical medical device that might be altered by having magnets nearby, then the bracelets should continue to have no noticeable effect on one's body.