Do you say "I mean" and "or rather" interchageably?
1 — used to emphasize a statement
▪ He has to stop drinking. I mean, he's going to kill himself if he keeps it up.
▪ He throws, I mean, really hard!
2 — used to correct a previous statement
▪ We met in Toronto—I mean Montreal.
3 — used when you are unsure of what to say or how to say it
▪ I'm not mad. It's just that, I mean, I think you've been acting a little selfishly.
2 a — used to introduce a statement that indicates what is true after you have said what is not true
▪ I don't like chocolate—rather, I love chocolate.
▪ What matters is not how often you call, but rather what you say.
▪ It wasn't red but rather a shade of bright orange.
b — used to introduce a statement that corrects what you have just said
▪ We can take the car, or rather, the van.
▪ My father, or rather, my stepfather, will be visiting soon.
The answer to your question is sometimes.
When 'I mean' is used to emphasize a statement or when you are unsure of what to say or how to say it, I wouldn't substitute 'rather.'
When 'I mean' is used to introduce a statement that corrects what you have just said I would use 'rather' interchangeably.
I wouldn't use 'I mean' to introduce a statement that indicates what is true after you have said what is not true -- at least not in statements you given
Others may not agree so I hope you get some further comments.