If I run 
```
ffmpeg -i input.mkV -c:v libx264 -crf 18 -preset slow -vf "rotate=90:ow=rotw(90):oh=roth(90),yadif,drawtext=fontfile='/path/to/font.ttf':fontsize=20:fontcolor=white:x=(w-tw)/2:y=h-(2*lh):text='%{eif\:n}'" -c:a libfdk_aac -delay -2.00 -itsoffset 9.84 -af "aselect='between(t,80,90)',asetpts=N/SR/TB" -movflags +faststart -map_metadata 0 output.MP4
```

And then I run
```
ffmpeg -i output.MP4 -c:v libx264 -crf 18 -preset slow -vf "rotate=90:ow=rotw(-90):oh=roth(-90),yadif" -c:a libfdk_aac -delay 0.00 -itsoffset -9.84 -af "aselect='not(between(t,80,90))',asetpts=N/SR/TB" -movflags +faststart -map_metadata 0 input.MKV
```

What is the result? does the 2nd command undo the first or does something else happen?
The results of running these commands are as follows:
1) ffmpeg -i input.mkV -c:v libx264 -crf 18 -preset slow -vf "rotate=90:ow=rotw(90):oh=roth(90),yadif,drawtext=fontfile='/path/to/font.ttf':fontsize=20:fontcolor=white:x=(w-tw)/2:y=h-(2*lh):text='%{eif\:n}'" -c:a libfdk_aac -delay -2.00 -itsoffset 9.84 -af "aselect='between(t,80,90)',asetpts=N/SR/TB" -mov flags +faststart -map_metadata 0 output.mp4
This will transcode the MKV to an MP4 file with a rotated video and audio track, using x265 for encoding and libfdk_aac for decoding. The rotation angle is set to 90 degrees (0 degrees = top left).
2) ffmpeg -i output.mp4 -c:v libx264 -crf 18 -preset slow -vf "rotate=90:ow=-90:oh=-90,yadif" -c:a libfdk_aac -delay 0.00 -itsoffset -9.84 -af "aselect='not(between(t,80,90))',asetpts=N/SR/TB" -mov flags +faststart -map_metadata 0 input.mkV
This will reverse the effect of step 1 above by rotating the video frame 180 degrees clockwise instead of 90 degrees counterclockwise. However, since this was done on the audio track, there may be some artifacts present in the resulting audio stream.