What is the interaction between Export settings and initial project setting?

I started a project in the wrong settings  (1080p), using 1440clips. but I want to export at max quality for YouTube - so 4k. 

I was able to export a 4k video , even though my initial project settings were set to 1080p. What kind of issues , if any, does this cause? 

I find it a bit unclear , how initial project settings interact with export settings. 

Ive spent 2 weeks editing this video, to only late realize that my setting were not correct - the auto detector interpreter by 1440clips as 1080, because there is no 1440p preset in premier elements. That's fine, because I want to export to max quality, 4k, for which there is a preset. However the auto detector downscales my project settings  1080p instead of upscaling my project settings  to 4k.  So it seems that I wineed to create a new project and choose he 4k preset. However, I then don't seem to be able to copy / paste my timeline from one project to another. Perhaps if I imlort all the same clips to the new 4k project, then I will be able to copy paste my timeline? 

Re- editing clips by hand in the 4k project  will take up to 30 hours  (almost a week of full time work) so I don't wanna travel that pathway. 

On the other hand, since I already exported a 4k video from my 1080p preset project, perhaps there is no further quality benefit in trying to make sure thetabmy initial project settings are 4k? 

Does it cause any problems if the initial project setting and final export settings don't match? Is changing the export settings similar to changing the project settings under the good ? 

How is it similar and how is it different? 

Any info on this topic is appreciated.