When you record a block in HearThis, the program does note what the text was at that point, so in theory it would be possible to detect later if the text changed. While that certainly feels like a pretty obvious feature – indeed, I thought maybe it was already implemented, or at least requested – I can’t find any evidence that it has ever been suggested. One slight difficulty is that not all text changes would necessitate an updated recording. (For example, a spelling correction or a punctuation change might not.) So there would need to be some way to tell HearThis to just note that the change was insignificant in order to clear the flag telling the user that a new recording was needed. We’re always trying to be careful not to over-complicate the user experience, so we’d need to think carefully about that.
Note that work was started (but has been put on hold) to try to deal with the more general (and more complex) case of changes that cause recorded clips to get out of sync with their corresponding blocks because of editing that changes the number, order, etc. of blocks. In one sense, your need is perhaps a subset of that, so it would perhaps be ideal to work on it as part of the larger problem. On that other hand, handling the simpler case first might be more doable and could at least serve as a stepping stone toward determining how best to handle the more complex scenarios.