yocto: rebuild part of project

Certainly, this is easy to do. Just specify the recipe you want to build instead of the image name, for example if it was the main gstreamer recipe you had changed (which at least in current versions is called gstreamer1.0):

MACHINE=some-machine bitbake gstreamer1.0

Note that the name expected on the command line is always a recipe name or something from PROVIDES in a recipe, and not a runtime package name.

Regarding devtool, it can certainly put you into an environment where you can more easily make changes to the source for a recipe and generate patches from them, but the actual building part we are discussing here doesn't really change. You can find more information on how to use devtool in the Yocto Project Development Manual

you can pass different command to bitbake based on what you need.

To remove temp:

bitbake -c clean gstreamer

To remove temp and sstate cache (I use this most):

bitbake -c cleansstate gstreamer

To remove download as well, and lets begin build starting from do_fetch and all

bitbake -c cleanall gstreamer

Once you are done with either of these clean, which ever suits you, you can simple give build command for the specified:

bitbake gstreamer