Locking an entity - considerations & implications?

We have a group entities in a foreign currency (RON) that we have sold part way through the year. My problem is forex on retained earnings (as an exmaple). So the forein group's earnings keep revaluing at parent currency (EUR) as the year goes on creating a forex loss/profit each month. However, this should not happen after sales date (say 30.6.). we should only realise the loss/profit as at that date with no change for the remainder of the year.

Can I simply lock the group of entities at Value EUR. Thereby locking the foreign group's results against EUR? Are there any implications at higher consolidation levels?