I don`t understand your problem, you can just update your text at the sync can`t you?, like this.
set text opaque:sync on:sync rate 40:hide mouse
point camera 100,100,100:autocam off
do
inc i
make object sphere i,rnd(5)
position object i,rnd(200),rnd(200),rnd(200)
point object i,rnd(200),rnd(200),rnd(200)
for m=1 to i
move object m,0.1
next i
text 0,0,"a message"
text 100,100,"another message"
text 200,200,"and another...no problems here"
a$=str$(i-1)+" : objects active and counting"
text 200,300,a$
sync
loop
Cheers.
Mentor.