Workflow multi-currencies conversion Proposal to Order

In our setup we have JPY as default currency and proposals are often in EUR or USD.
Due to current currency fluctuations, we update daily the currency values.
When we sign a proposal for 100 EUR which (which is let’s say 14,000 JPY) and convert it to an order, the JPY value stay fixed on 14,000 JPY but the EUR price changes to 99 or 101 Euro.

This is undesired behaviour for us, as I like the EUR price which we agreed with the customer to stay fixed and have the JPY price fluctuate. Is there any setting to change this behaviour?