Enable Currency Field on Opportunity Screen without choosing a Business Account.

Hi @j1o2s3h4u5a6,

You can do the following customization to enable the currency fields,

    public class OpportunityMaintMultiCurrency_Extension : PXGraphExtension<PX.Objects.CR.OpportunityMaint>
    {
        #region Event Handlers
        public class MultiCurrencyExt : OpportunityMaint.MultiCurrency
        {
            protected override CurySource CurrentSourceSelect()
            {
                CurySource CurySource = base.CurrentSourceSelect();
                CurySource.AllowOverrideRate = true;
                CurySource.AllowOverrideCury = true;
                return CurySource;
            }
        }
        #endregion
    }

Also, attached the customization project for your reference.

Hope that helps. Good Luck.!