I have used the term evergreening
in the context of replacing PC systems at a pre-determined rate; that is, that such a scheme would replace every PC in an office every 3 years by gradually replacing systems a few at a time over an extended period.
I cannot however find this word used in this context in dictionaries online and I'm not sure if it's a colloquialism in the IT field or if it would be recognized in the general populace. If the latter, what are some alternative terms?