These three replaced Jason, Zack and Trini after they decided to attend the Piece Conference. After these powers were lost, they were turned into children. After they regained their teenager form, Aisha moved to Africa, Rocky became the Blue Zeo Ranger and Adam remained on the team as the Green Zeo and Turbo Ranger.
After her evil spell was broken, she replace Kimberly as the Mighty Morphin Pink Ranger after Kimberly decided to attend the Pan Global Games. Just like the other 3, she was turned into a child. After regaining herself, she stayed on the team as the Pink Zeo and Turbo Ranger.
These 4 people replaced Tommy, Adam, Tanya and Kat as the Red, Green, Yellow and Pink Turbo Rangers. However they lost their powers after being beaten down by Divatox. They followed her into space only to be found by Red Space Ranger Andros who gave them the powers of the Blue, Black, Yellow and Pink Space Rangers.
Formally evil queen Astronema, this person replaced Kendrix after she was destroyed by trying to destroy the Savage Sword. She went with the Rangers to the "Quasar Stone" and relived her powers by putting her sword into the stone. Soon after Kendrix returned, she thanked her for taking her place.
So, what now? Will the Red Samurai Ranger be replaced by a female like the Sentai counterpart Shinkenger? Only time will tell.