I edit profiles all of the time to suit my needs. Some modifications can indeed cause unintended results and are usually coded a certain way for a reason. If you are not comfortable making extensive changes to a profile it is probably best to not do so, but this is a fairly simple edit that really cannot harm the profile. It is fairly standard for users to edit the Mail/Vendor settings in profiles to suit their needs. Keep in mind that many of the Mail/Vendor settings share a relationship but this really only applies to BOE items. In other words if you set "Mail all BOE Greens to: True" you should change the "Sell all BOE greens to: False" and so on. In the case of BOA epics simply changing it to true should be fine.
If you run into any problems feel free to PM me or ask more questions in here. I am at work right now so I cannot do any testing, but I can when I get home. Also its always a good idea to make a copy of the original and stash it away someplace safe in case you damage it beyond recovery in editing you can always go back.
Edited to include: Also please keep in mind that by changing this setting to true, it will vendor all Purples in your bags so make sure you do not have 2nd spec gear or extra items you want to keep in your bags. You could add things to the protected items list, but that is another can of beans. Its always good practice when farming instances to keep your bags completely free of anything you want to keep. I'm sure you have already thought of this but I just wanted to put the reminder out there.
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