Make usb stick bootable while keeping files

I am learning how to install an image on my USB stick and make it bootable using the rufus software. But, I only have USB sticks with data, and want to keep them there. Is it possible to somehow install the OS image and make the USB stick bootable while keeping the existing partition and the data on it?

PS: don’t want to resize the partition either, that’s risky operation.. just wonder if there’s an option where the image can be installed within an already established partition.