The first question that should be address is the latter. Exclusive fidelity to a group of deities owes more to monotheistic thinking than to polytheistic theology or political conditions, something which in the past could have forced people to concentrate their practices on a national pantheon. But even still there would have been room for personal devotions to foreign gods, some of which could end up in the official religion of a particular city or country. So unless you’ve taken an oath of exclusivity, promising to worship one or a particular set of gods alone, there’s no reason why a polytheist should feel theologically compelled to pay homage to a single pantheon. In fact, diversity is only to be expected in a religious system that recognizes no limit to the number of divinities and further acknowledges the existence of “gods of place”.
This being said, how to work out the cultural diversity of one’s personal pantheon? Where does it leave us in terms of community? Is one a Celtic polytheist while actively worshipping Celtic, Norse, and Roman deities? And not counting syncretism, i.e., without blending those gods as cultural versions of each other (which is a possible answer to the questions). Perhaps an analogy can provide us with a framework, namely the distinction between community, partnership, and friendship.
Community refers to your native or adopted nationality. It implies a country of which you are a citizen, the laws you’re ruled by, to whom you pay your taxes and who are your communal representatives. By partnership I mean a close relationship with someone, either with the official status of marriage or civil union, or just a long standing companionship with no legal bond. Friendship is simply a non-exclusive link that can take many forms with various degrees of intimacy.
It’s true that this, as all analogies, is not without its limitations and grey areas. For instance, one can have double nationality and being a citizen of a country doesn’t imply that he or she has a particular cultural background. The United States is full of communities that are both American and something else (Jewish, African, Asian, etc.). Regarding the former, it will be addressed further on; on the latter, however, for the sake of argument, I’d like to focus on nationality in the sense of the laws and representatives that run your life, regardless of cultural background. Overlapping between the three elements will be dealt with at the end. And before this starts getting confusing, I’m going to stop and leave the translation of the analogy to a second post.