Portfolio sizes

I have three different sub portfolios with different relative target sizes:

Portfolio                      Target size          Actual
Global momentum        75%                     86%
Trending value              20%                    10%
Opportunities                 5%                      4%

I am planning to increase Trending value and reduce the Global momentum closer to their targets. My idea is to do this gradually as stocks are replaced in Global value. When a stock is replaced (according to the rules), I increase the amount in the replacement stock and sell off the corresponding amount in the Global value portfolio.

With this approach I expect to come closer to the target sizes within a half to one year from now. This depends of course also on the relative performance of the portfolios from now on.