How to change a Party in a validated statement

A validated statement was entered with an error on a Party. This can happen because the previous Financial Year was not dealed in Tryton, so there was no Invoice to confirm the choice of the Party. (It could occur too if two Parties had an invoice of the same amount).

I don’t see how to correct the erroneous Party. Cancelling the Statement, then passing it to Draft to correct the Party leads to the loss of all invoices in the Statement.
(I use Tryton 5.0)

I tried on demo 5.0 and cancelling—reset to draft does not remove the invoice on the statement lines but only the line for which the party is changed.

I did it using sao, but you’re right it doesn’t seem to be the cancelling action that resets the invoices.
I was able in sao to change Party on a validated statement (in a “line edit mode”), and this step deleted other lines’ invoices. (Just tested again on demo).
But the party changed this way doesn’t persist in some way (the Reconcile wizard still presents the old party). The behaviour is not the same in the GTK client (no party edition).

Normally line edition should be forbidden on validated statement and this is the case on latest version.