yes this methode is cold:
1- if you are changing the neumber of neurons from N to n where N>n: this is called :'constructive' learning
2- if you are changing the neumber of neurons from N to n where N<n: this is called :'distructive' learning
but retraining alwayse requeired , not from the begining but from the final weights that u have in final net
if you want to found some papaers in this area use this key words :
neural networks with additive hidden nodes ; distructive neural nets .....etc. good luck.