Othrs may have a bit more info on this, but there was timeline with regards to Chavous playing CB and Safety.
He was used as a CB in the playoff year, If I remember correctly... and played quite well. In the following offseason he lost some 15 lb. to improve his speed, quickness to continue to play CB. I doubt that he did that without the approbation of the Coach, and the full expectation that they wanted him to play corner.
His shortcommings as a corner started to show in year two... and we certainly heard that coaches would prefer to have him a safety, even though, at the time, there was no clear-cut better replacement for him a CB.
I would imagine he also considered that his contractual value on the open market would be greater if he was projected as a CB, not a Safety. And, given the contract he received frm Minny, he was certainly right.
Almost as soon as he got to Minn. there were reports that coaches were dissatisfied with him at CB... and fairly quickly moved him to Safety... but, lest we forget... Chavous is a Safety making Cornerback money... and the offer he received from the CARDS was no where near that of the Vikings because, amongst other reasons, they wanted him to play Safety.