400w mh to t5 switch for veg

i got 8 plants under a 400w mh. 5 are blackberry kush clones and 2 lemon purple and a random strain. i want to keep the lemon purple and random strain in veg while the other 5 go into flower. i gonna put the lemon and random under 4 bulb t5 lights for 18hrs. my question is the change in light intensity wont mess with the plants to much will they?
 
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