I've been noticing for the last couple weeks that my back hasn't fully recovered from my back workout (Tuesday) before leg day on Friday. When doing SLDL's to target my hamstrings, my back would get tired much quicker than my hamstrings. Yesterday, I decided to modify SLDLs to better target the hamstrings. I put a 15kg oly plate under each foot and then limited the range of motion on the SLDLs to a little beyond the bottom half of the normal movement. My hamstrings got a much better workout, as evidenced by the way they are feeling today. 
Are there any ill effects to doing this? Anyone else tried something similar?

Are there any ill effects to doing this? Anyone else tried something similar?