Good to hear you found some time to look into it ;)
Quite the opposite, thanks for the patience :)
Would that mean that once variable is created (without history being enabled) it won't be possible to alter it?
Yes, it won't. However, what I wanted to point out with my extract from ScopeInstanceImpl.setVariable is that it ignores the historyEnabled parameter if the variable already exists. I do not know whether it makes sense to enable/disable history for an existing variable. In any case that would be a feature request that we can defer for the time being.