Sorry we don't return relics within 4 days if they are used on items. 4 days policy is about buying something by mistake, like missclick or being confused. Relics are one of the "return within 4 days" exceptions because user can not accidentally buy (first confirmation) and use (second confirmation) relic at the same time, these actions are certainly intentional and user takes all responcibility for them. There are more exceptions like transmog items and used services like refraction, sexchange or rerace.
We don't actually replace items because of the "change of heart", there will be too many returns in this case and we won't be able to cope with them.
Nevertheless if relic doesn't flash heal properly we will return all tokens. Bugged items can be returned regardless of time and item type . Please give us the link from wowhead on your relic and tell why do you think it doesn't function properly, so that I could ask testers and developers to check it.