If we have RFQ in USD, can we change it to Euro while recording vendor quotation?
Very much. You can change currency and also terms of delivery while elevating request for quote (RFQ) to vendor quotation. This is a practical situation. You might have sent RFQ to your vendor in one currency but he might send you quotation in another currency.
Just want to add something here. In RFQ, currency is optional. You do not need to specify currency in RFQ and in most of the cases you won’t. Normally RFQ contains the list of items for which the vendor is requested to provide a quote. Vendor might quote for any or all the items on the list in any currency. Shipment terms field is more relevant as you can request the vendor for any terms, however, he might change that too or give you different quotations for different terms. He might give you one rate for Ex-works, another for CNF, CIF, FOB or so on. Therefore, to sum up:
Currency filed is available in the RFQ but is rarely used in template to instruct the vendor. It is still useful to specify expected range of price, if you are using that.
Shipment terms field is almost always used, but it does not restrict ERP from accepting quotations for different terms. Such restriction, if at all required, has to be imposed by policy.