can i change from cfl/t5 lights to hps on 28th day of flowering or....

should i just leave the lighting alone. I want to change out for a 600 watt hps. I only have 2 plants and they are doing fine but they are about a little under 3 feet tall. I have 4 54 watt t5s which are 4 feet long each. another single t5 which is 4ft on the back wall and about 10 26 watt cfls. lower buds are not getting much light. This is my first grow.

if u have a dimmable ballast that would workr best then u can keep it lower for a week or so and bump it up otherwise if u just kick them into it right away u might burn then up