If you are going to increase apprenticeship units, serifs at the time of Promotion will be a problem.
The function handling their dialogue is FE8U: 080CD7FC.
This routine appears to branch with Unit ID.
080CD80C 2812 cmp r0, #0x12 //if (id == 0x12 (Amelia) )
080CD80E D007 beq #0x80cd820
080CD810 2812 cmp r0, #0x12 //if (id <= 0x12 (Amelia) ) Probably ID 0x09 Ross branch
080CD812 DD09 ble #0x80cd828
080CD814 2818 cmp r0, #0x18 //if (id == 0x18 (Ewan) )
080CD816 D005 beq #0x80cd824
080CD818 E006 b 0x80cd828 //Other than that, ID 0x09 Ross
If you want more than three people to appear, you will have to rewrite this function.
Or would you use Ross's lines as a generic line of speech.