i have an converted .mp4 video file (or .m4v) + an
Is there a way for me to embed this
.srt file into that mp4 file without running a complete convertion?
What you want to do is generally called muxing or re-muxing.
Have a look at Subler, it should be able to do what you want. Open your video file, then drag the srt onto the screen and save as new file.