[Heliod]

Let's take the INTJ and ISFP for this question.
The functions of the INTJ would be Ni > Te > Fi > Se, and Fi > Se > Ni > Te for the ISFP.
Now the typical career where the INTJ function order would be ideal is likely applied physics. Taking abstract concepts grasped by the Ni and apply them to reality via Te. But the ISFP also has Ni and Te as his functions, although they are inferior. Let's say the ISFP pursues a career in applied physics, where it's inferior functions would be used and with that I assume also develop. Would after a certain amount of time those functions become the primary functions, even when not working on some sort of engineering project ?

[knittigan]

No. Even though you can become more comfortable/skilled using other functions, they are never as comfortable, instinctual or as natural as your dominant/auxiliary. You can outwardly appear more/less like a different type, but you'll never actually <I>be</I> one, savvy?

ETA: What you're describing is simply becoming a more well-rounded individual.

[Neon Knight]

I have seen several references about well-roundedness. Like in my case I've been typed an xSFP of some sort for a long time and it's been suggested that I'm just a well-rounded xSFP. I can see if you are about equal in expressing the top 2 functions and then the bottom 2, but I can't see it in all 4 being all over the place.

The good thing about function theory imo is that function development, stress and mental health are contributing factors to one's behaviour and aren't an expression of changing type at all. I have a book I highly recommend called "Was That Really Me?" by Naomi Quenck who explains that people often have jobs or prefer recreational activities that require people to use their less preferred functions, but again this doesn't change your type or which 2 are your preferred functions.

[CeeJae_Flippert]

You know how some people start to rub off on other people the more time they spend with them? Whenever I spend time arround certain people I end up acting like them, this may have something to do with my tretiary and inferior functions being used more when arround these people. lets say theres an ENTP and an INFP interacting, the INFP may start to act more outgoing and use their tretiaty T more then they normaly do, to match the ENTP.

[LiquidLight]

You know how some people start to rub off on other people the more time they spend with them? Whenever I spend time arround certain people I end up acting like them, this may have something to do with my tretiary and inferior functions being used more when arround these people. lets say theres an ENTP and an INFP interacting, the INFP may start to act more outgoing and use their tretiaty T more then they normaly do, to match the ENTP.

Well humans are communal creatures by nature and there is a degree of cooperation (submissiveness/conformity) that goes on that isn't really related directly to personality.

But what you describe is actually much more common for people with a preference for Fe (since Fe is reliant on the world around the individual). Lots of Fe types (especially extraverts) can become almost chameleon-like molding themselves to expectations of whatever environment happens to be most important to them at the time. Its not so much the environment rubbing off on them, so much as the Fe type consciously making an effort to bring himself into alignment with that external input.

INFP would be one of the least likely to have something like this happen because they are so dependent on their own sensibilities, which is one of the reasons they can have such problems with being sociable. They're not always shy or anxious, they just may be unsure of what the prevailing social conditions are (where a Fe-dom would immediately know). In your example, the INFP and ENTP would find common strength through Ne and maybe Si but my guess is that because of tertiary-Fe, its the ENTP who would move toward being INFP-like (as much as he can, they only have two common functions and Si isn't strong for either of them).