No it's not safe and downright rude to remove other tasks because your program does not OWN them! :-)

The only safe way is for the other programs tasks to terminate or for the system to remove them for you.

However, in AmigaOS, there is not only tasks but processes. Tasks are more low level, suited to device drivers and can't use some DOS functions or other functions. Processes have extended functionality and can call all functions. A normal application would run as a process.

Now, that said, assuming a task (or process) is causing you trouble the best course of action would be to try a utility like Scout. First try to send it break signals. If that fails you can freeze the task or tell it to remove it.

Now as this is a programmers forum I take it you want to be able to do this yourself? IOW duplicate what Scout would do. You could perhaps do a bit of task hacking and change its fields to modify its behaviour. For example cause it to be kicked off the running/ready list so it is put onto a non running list. Or brutally lower its priority. Don't recall what functions OS4 has but you could also try to kick it off as the running task by adding an interrupt server, such as vertical blank, and in interrupt check for the task then call the Switch() routine on it if found.