As far as ATC around Europe is concerned FPL alternates are of little interest. The only time they matter is if an aircraft goes radio fail or, more likely, if its whereabouts are not known for some reason - the FPL destination and alternates are the first places to check.
In practice, there are commercial constraints too. Most of the busy airports will not accept an ad-hoc arrival but if you say to ATC that you wish to change your FPL and div to XXX, in the absence of slot restrictions etc. a couple of phone calls will often be all that it takes to sort it out. We're good like that in ATC!