Because microlights are generally sub-ICAO, and in Europe also Annex 2, which means not subject to EASA control - this comes entirely under national authority discretion. In the UK the only legal aerial work in microlights are instruction and test flying. However, Spain could well be different - and I did once see a microlight in Spain towing a banner advertising a bullfight.
So, it may be legal in Spain, but that is entirely down to the Spanish.
There must be a Spanish national microlight association and a national aero club. They should be able to answer the question.
G