[helene_t]

 Vampyr, on 2019-January-10, 11:12, said:

Not in real bridge, but online should really have its own set of laws.

You are right, of course. Partner had not called yet.

[nige1]

 gordontd, on 2019-January-10, 11:18, said:

I understand they are currently being worked on.

 nige1, on 2019-January-11, 10:44, said:

According to F2F law, the auction is illegal but, IMO you nullify your generosity in permitting LHO to correct his opening bid, if you now take advantage of the UI from your partner's cancelled overcall (i.e. it's UI morally if not legally).

 Vampyr, on 2019-January-12, 20:16, said:

The auction in not illegal in live bridge. You'd have a tough case to make, though, that it was truly a mispull.

 helene_t, on 2019-February-10, 18:54, said:

You are right, of course. Partner had not called yet.

The current on-line framework seems a vast improvement on the f2f laws, so it might be better to change TFLB than spoil the online protocol.
Thank you, Vampyr and Helene_t, for correcting my mistake about f2f law
I accept that if you allow LHO to change his call from 2♦ to 3♦ then partner's cancelled 2♠ call should be UI to RHO but AI to you.