Retroactively apply HR zones to recorded activity

The state of the HR Zones at given moment is saved in the FIT file of the activity. You would need to export all corrupted activities as "Original", and edit them with a FIT compatible editor, such as for example the FFRT, and then importing back the edited files (after removing the originals)

solved

sadly using FFRT will not influence 'my other metrics'

That's true. Just the HR Zones. But most of the metrics is influenced by the wrong real time HR more than by the HR Zones anyway.

So even doctoring the fit file and re-uploading it won't affect things like load and Training Effect?  

It seems like the Training Effect uses a combination of HR zone and power.  For instance, today I did some high power anaerobic reps, but the anaerobic training effect said 0 (I'm guessing because I never broke out of what the computer thought was HR zone 3).

solved

I would just delete all messed up data permanen

Just note that deleting the activities alone will not remove all the metrics like VO₂max, etc. A lot of metrics is being stored separately, for example in the daily monitoring files. So additionally to the activities, you'd have to delete also the Daily data for the concerned days (see the menu on the Daily Summary page). Thought that would mean you would lose also all other metrics like steps, calories, IM etc (some of them are wrong anyway, though, due to the wrong HR). Theoretically you can export the entire package of the daily data (it is a zip package with many FIT files), and import some of them then back, after deleting the day, but it does not always work in the way one would expect. And some of the data is grouped into the same file, so not easy to separate it.

Personally, I'd rather suggest just correcting the current state of the HR Zones, disabling the Max HR auto-detection as Former Member suggests, and going on - all the metrics will settle down to the true values after a few days, maximally weeks in some cases.

Agree, if there isn't a sane way to retro all the data, best to just let it 'wash away.' 

As for the auto-detect, for the longest time I thought I knew my HR max.  But then one day after a long rest period, I exceeded it by an appreciable amount -- and again a week later.  The auto-detect summarized it when I concluded the activity -- certainly wasn't paying attention to the HR value when pushing hard in those sprints.  I thought it was nifty how the zones automatically adjusted.  

I'll just turn it off and try to notice any new highs in the activity data, then set any new max after-the-fact.  

An occasional peak in the HR is not necessarily the right max HR. It is safer using some methodology to determine it. Setting it too high, you risk harming yourself or harming your training, if you then do HR based workouts. Have a look for example at the following video for some ideas: