I know I can add a larger SD card, and I know that I could even make the SD card behave as "internal" memory. But there are performance issues. Access to the SD card is slower. My question is, can I install a larger internal memory chip? I suppose the biggest hassle would be transferring the bootloader, OS, etc.
No, you would not be able to. And, that wouldn't make the SD card work better. Also, on that device, as it comes, you would not be able to make the SD card "Internal" storage. For one, the OS needs to be 6.0 or newer, which that device doesn't have (unless you were able to upgrade to it) and two, that particular manufacturer doesn't really allow for the option to make the card "Internal" storage on its devices. So to do so would require a lot of changes (rooting, etc.) which could brick the device.