Yes exactly, but where you can only use live trading to inform you of the parameters. I'm conscious of using a naive method that may overfit. I can handcraft a prior, but still need a reasonable posterior.
There's no reason why in theory you shouldn't use the same methods you'd use for a backtest (bootstrapping, bayesian...), but of course your return history is much shorter (unless you've been live trading for donkeys years with an unchanged system), and hence you're extremely unlikely to be able to distinguish between different strategies (unless you are a high frequency trader with a high single digit or low double digit Sharpe). This means in practice you're likely to recover your prior.
GAT
I've already given almost half of it back in the last couple of days (7.2% DD from HWM @ 25% vol).