I'm wondering -- DeCal says "If I purchase a CC merchant account with [from?] enom" -- offhand, I don't see where you can "purchase" one. Do you mean the CC account that enom provides that can be used with RR and PDQ?
If so, then here are some observations on my part -- when you set up your prices, for RR for example, I only see where you can specify prices in US$. The RR interface/page will present an order page with the prices you specify, again in US$. I do not see anything anywhere on the enom site or RR page regarding other currencies or currency conversion.
I also note the following -- eNom's User Agreement for Merchant Services says, "The Service provides merchant services and templates for you to register domain names and offer other products and services. " It later says, "Unless otherwise stated, all fees are quoted in U.S. Dollars. " Frankly, I do not see anything anywhere "otherwise stated." It also says, "Users agree not to use the RegistryRocket Service for cash advances, or sale of goods not expressly authorized by the Service." Although, this last sentence refers to use of RR and not the merchant account. (I want to ask, how can you use RR for other things? You don't have much control over what RR offers.) Also, it is unclear to me which "goods" are "expressly authorized by the Service." If you ask me, other than domain registrations, I don't see anything "expressly authorized." However, I am going to assume that the other services that enom provides, such as name-my-phone, would be included in permissible offerings under the first and third statements I clipped.
The first statement I clipped refers to use "to register domain names and offer other products and services. " It is not specified what the "other products and services" are or are limited to. Again, with regard to RR and PDQ, I think you are limited to what is offered via enom's site and the RR interface.
So whereas this is not a definitive answer to the questions, it appears to me that there is no way to specify a currency other than US$ and that you are limited to using the account to product/service offerings that are contained on enom's site or the RR page.