In your example text, the word
except is used as a conjunction and it could be replaced by the conjunction
only — as you suggest — with very little change in meaning. The difference is nuanced and a matter of preference. So it is your choice:
"Picture James Bond, except without the British Accent."
"Picture James Bond, only without the British Accent."
Your second question, about
or is harder to answer. Because the two words have very different meanings (as noted by Crosscounter), it is usually easy to decide between them: do I want both (cookies and milk) or do I want one (cookies or milk)?
In the text you are examining, there is nothing so concrete to guide us, since I am without the items described. This may be another matter of preference, but I have a strong feeling that
or is better. I cannot find a rule to support my preference, but here's my logic:
In English usage, there are word pairs that belong together, called correlatives. These include both—and / either—or / neither—nor. It seems to me if you use
and you imply the word
both, and if you use the word
or you imply the word
either. When I ask myself if it should be "without either a British accent or a six-pack" or "without both a British accent and a six-pack", the word
either emerges the clear winner.
So, with the understanding that my logic may be flawed, and this may actually be a matter of preference, the word
or is preferred:
"Picture James Bond, except without the British accent. Or the six-pack"
"Picture James Bond, except without the British accent. And the six-pack"