If you want to change the usage for which the fraction is intended, you must first request permission to change the CH license at the City Hall.
Secondly, You will need to have the agreement of the Condominium!
And here there are two distinct possibilities:
A) If the title constituting the horizontal property (TCPH) refers nothing about the usage of the fraction, then an approval of two-thirds of the building neighbours/owners is sufficient...
B) If, on the other hand, the TCPH defines the usage of a certain fraction, then the approval of ALL condominium neighbours/owners is required.
If the latter applies, the change of the destination of the fraction implies the alteration of the TCPH.
And the law defines that its amendment is obliged to the execution of a public deed, drawn up by a notary, or a private document authenticated, by a lawyer.
Please note that this information is not a substitute for professional legal and financial advice and no liability can be accepted for any kind of loss or damage.