Translate one entity during one year against different avg rate

Summary

Is creating a local rate account the best way to deal with an entity that uses a different exchange rate during one year?

Content

In the middle of the year an entity is bought. Data is only reported once a year. Because of this a different average exchange rate must be used in the year of  the acquisition. The closing rate is not an issue. This different rate must be used in all calculations where you normally use average rates: movements and P&L data.

How is that arranged best? I can think of giving that entity permanently a different currency, but that means you will drag this 'issue' on forever. The other (better) option seems to me to create a local rate account and create translation override rules with that. Is that the way to go?