I think i've found a solution, if you want only a few units to burrow.
1. Have a player (say player 7) who is a computer- and has burrow researced.
2. Place a location (say "Zergling Burrower") and have it so in a start trigger:
3.
-=Players=-
7,8 (player 7 and 8 should both be computers, player 8 is ur main enemy)
-=Conditions=-
Elapsed Game Time is
at least 0 game seconds
-=Actions=-
Move all <zergling, hydralisk, lurker?> at "Burrow1" to "Zergling Burrower"
Move all <zergling, hydralisk, lurker?> at "Burrow2" to "Zergling Burrower"
and so on- make sure u dont have giant big 1s cause u have to move the units back later
Give all <zergling,hydralisk, lurker?> at "Zergling Burrower" For player 8 to player 7.
-Wait for <100-200 milliseconds>
Give all <zergling,hydralisk, lurker?> at "Zergling Burrower" For player 7 to player 8.
move all <zerglnig?> at "Zergling Burrower" to "Burrow1"
move all <hydralisk?> at "Zergling Burrower" to "Burrow 2"
move all <lurker?> at "Zergling Burrowre" to "Burrow 3"
<DONT PRESERVE TRIGGER>
Comment: Zergling Burrower BETA ( Thank u so much Conquer)Fa(

)
-= End =-
That should work.