hbsag mutant can be confirmed by hbsag architect by abbott or hbsag by siemens or roches, not by old assays which are still used in US, canada, UK
hcv usually suppress hbv but doesnt eradicate it toatally, you should get rid of hcv first by interferon+new antivirals combo and then take care of hbv by hi sensitivity hbvdna pcr to determine if it is eradicated or occult
while hcv is present it usually makes no harm like in your case where hbsag is negative and hbvdna undetactable (if hbvdna is detactable you have hbsag mutant)