A crossover of sorts with the Unwind series by Neal Shusterman.
In a world where Nightmare Moon won the war, there was a time where an uprising of rebellious teens made life unbearable for everyone, causing crime rates to skyrocket. To fix this problem, a chilling new law was created.
Between the ages of thirteen and eighteen, parents can have their child "unwound," whereby all of the child's organs are transplanted into different donors, so life doesn't technically end. While most of the teens unwound are troublemakers, there are exceptions to the rule.
Glowing Flame is a fourteen year old colt who is an orphan with a bad attitude. When the orphanage experiences cutbacks, he is made part of a group from the orphanage scheduled to be unwound.
Meanwhile Sweetie Belle gets into a terrible accident, and needs part of someponys brain added to hers. When Glowing Flame’s mind joins Sweetie Belle’s, there will be no limits to Flame’s wrath.