PLASTIC

moldable, pliable, not rigid

capable of being molded or modeled (especially of earth or clay or other soft material)
SYN - tactile
"plastic substances such as wax or clay"

capable of being influenced or formed
SYN - pliant
ANT - inelastic
"The plastic minds of children"

"The teachers found that if they made clear on the first day that the rules weren't plastic than the students wouldn't try to test them all the time."

"He enjoyed seeing a student like him who had learned so much yet at the same time still had a very plastic mind."

"he knew he wouldn't worry too much about the suit, it was plastic enough that they could fix anything wrong with it later."