Is it possible to write such a bootloder, that will change only part of program? For example: I have module foo that is doing something and i would like to update only its behaviour. Bootlodaer would be one of ongoing tasks and it would react for incomming packets (eg from bluetooth module), store them in some free space in memory and form new module foo1. When it ensures that formation of foo1 is complete (checksum is correct) it tells sheduler to switch from foo to foo1 and frees memory after foo

I think this is more of a general embedded programming related question, than something specifically about using FreeRTOS. Note that that FreeRTOS applications are normally statically linked, so it would a lot of effort to try and dynamically link at run time compared to just replacing the entire application as a firmware update.

As RTE said, this isn't a FreeRTOS issue, to my knowledge, nothing in FreeRTOS prevents, or supports this sort of action. (Being in a multi-threaded enviroment like FreeRTOS provides does raise some issues, but that isn't FreeRTOS specific).

How you do it is very system speciflc. Normally you need to build your program specially so the changable section is put into a seperate section of memory, so you can just update that piece. You also need to make sure that everything in that section that is accessed by something outside that section doesn't move.