Sometimes it ends well, though.
Puyol was a poor RB turned into our best CB ever.
Xavi started as a defensively weak Cdm transformed into one of the best Cms ever.
Rakitic was a Cf and Amc turned into a workhorse Cm for our team.
Roberto was an allround midfielder, turned into a good RB, as it seems.
Mascherano was awesome Cdm, turned into a very good Cb for our team.
Marquez was a Cb who played as a Cdm for the whole season when we had injuries at Cdm for Edmilson and Motta (we even won a title).
There are lots of other good and bad examples.
These transformations don't always end bad.
I have read a few days ago that Halilovic will now play in his new team as a Cm and Acm, not as a winger anymore.
His new coach wants him to create from midfield and to have ball as much as possible.
It happens all the time.
But with Gomez the only thing of his that fits in DM is height,
the rest is all CM/AM material