You need a subscription to the OEM documentation supporting the activities/types on your Part M/145 cert. However mandatory mods do not have to be done through Avantext. You can monitor these manually via the websites of FAA, EASA, etc and the authorities will be OK with it as long as you can demonstrate you are in control. Note however any change in the means of control will have to be reviewed and agreed by your surveyor as this is what is currently approved.