I want to talk in an American accent but how can I transition into it slowly for people who know me without them noticing a sudden change?

As strange as it may seem, I hate my accent and want to speak like an American because I think it sounds cooler and more like how I want to sound.

I've more or less perfected my version of an American accent on my own, I think.

But whenever I'm with other people who know me, I revert back to my old accent instinctively because that's how they know me to sound like. I'm unsure about how I can subtly transition without them noticing a sudden change, such as through gradual exposure to my accent changing more each time they hear it. That way I could argue that I don't know how it happened and it was a slow progression if they eventually realise it's different, rather than something forced that I started doing one day.

The biggest thing I think is changing the pronunciation of certain words with "a", such as going from "fahst" to "faast" for the word 'fast', or "mahsk" to "maask" for 'mask'. Because it's really one or the other, there's no in-between. I feel like for most other sounds, a gradual transition into more American sounds can be possible, but that one's like, how can I make the plunge and will people notice it straight away and think it's weird?