Earlier quoted context omitted.
Hem, not... this is not how it works in Spain. Maybe a local exception, but not the rule. The law is very clear about it.
If you know some locals who own apartments in the metropolitan areas, many will be open about their different modifications they have done without proper permits, because it's so damn hard to actually get the permits. Yes, the law is very clear about a lot of things, but what happens in reality is often not so clear always.
Permits for modifications in extant buildings can be also hard to obtain if the area is historical and buildings are singular, old or protected for some reason. Specially if you want to mess with the load that the structure must stand. Out of this areas there is often a 'permit free' period in Abril-May for doing small repairs and repainting.