in odoo 12, you can directly change the display of currency (in currency setting) once activate the developer mode.  

Ok I found how to do it.

You need to install accounting module, activate multiple currency and then go to sales - setting - pricelist.

Add the desirable currency.

From there on, currency can be changed on the quotation page.

Hi Noris,

To remove currency symbol remove

t-field-options='{"widget": "monetary", "display_currency": "o.currency_id"}'

And now about default currency you are changing but its not affecting in invoice report.

that is just because invoice report is loading from "Attachment"

for that do following steps:

Go to Setting > Technical > Reports > Reports 

Open Invoice report.

And Unchecked "Reload from Attachment" if it is Checked.

I hope its helps you.

Hi Noris, the simple fast solution is to modify it directly on the DB, go to your DB ==>res_currency and change it manually, refresh you application, and everything is gonna be well.