That is kind of an interesting story. When I swapped Tripod mode for ATTI mode, I watched this video:
The information provided in the video was perfect for swapping Tripod mode for ATTI mode. However, when I went to swap Sports mode for ATTI mode I discovered the information provided in the video was not correct. I found the following in a comment (DISCLAIMER: I have not verified all of these parameters):
Flight switch position parameters
fswitch_selection|g_config_control_control_mode[0] = Tripod : factory value = 12 (Tripod)
fswitch_selection|g_config_control_control_mode[1] = Sport: factory value = 8 (Sport)
fswitch_selection|g_config_control_control_mode[2] Position (GPS): factory value =7 (Position GPS)
Switch parameter values
0 = Manual Mode (GPS position and Altitude Stabilization are disabled)
1 = GPS - no noticed difference
2 = GPS - no noticed difference
3 = ATTI Mode (Altitude Stabilization)
4 = GPS mode indicated, sport mode speed for some reason
5 = GPS - no noticed difference
6 = Beginner
7 = PGPS Mode (Normal)
8 = Sport Mode
9 = FARM Mode (Altitude stabilization with RTH capability)
10 = GPS - no noticed difference
11 = GPS - no noticed difference
12 = Tripod mode
So, to answer your question, all you need to do is change fswitch_selection|g_config_control_control_mode[1] from 8 to 3