Well, if you are trying to persuade Madrid to change the constitution, so as to allow secession, you are in a for a long haul. It reminds me of Irish Home Rule, which was discussed for decades. In the end, Irish people cut the Gordian knot.
Doing it legally is very difficult. The Belgians went in for strikes, street riots, occupation of public buildings, desertion of troops, the famous 'night at the opera', and so on. Different times, of course, (1830).