As far as I can tell, 'Cortez The Killer' was not fully banned in Spain, though it is possible, I guess, that it might have been banned from airplay on Spanish radio stations. Young didn't release 'Cortez The Killer' as a single, seemingly, either in Spain or elsewhere - it might have been a little long as a single, at 7 minutes and 30 seconds. The song came out on the album Zuma, released in November 1975. 1975 was very much a transition period between Francisco Franco and the subsequent regime, seeing that Zuma was released the same month that Franco officially was declared dead, after having been ill for a couple of years.

Zuma also appears to have been released in Spain at the time, with the contents of the audio being unedited. There was, however, censorship of a sort: 'Cortez The Killer' - a song lamenting the loss of indigenous Mexican culture thanks to the conquest of the Aztecs by Hernán Cortés - was renamed 'Cortez Cortez' in Spain, as you can see in scans of the Spanish version of the artwork for the album (under Francoist Spain, apparently, Cortés was seen as a hero).

But broadly speaking, the fascist Franco government aimed to control artistic work and thus censor things that didn't comport with its traditionalist ethos; in my searching for academic papers on this topic, for example, I found plenty of academic papers on things like the censorship of film and political theatre in Francoist Spain, or on the censorship of the books of James Joyce during the era. Zuma, being at the end of the Francoist era, probably got away with a lot more than if it had been banned in 1971.

In contrast, an article in a popular Spanish language newspaper, El Pais, argues that late Franco-era censorship of popular American music was inconsistent and based on a lack of understanding at times; the censors were keen on censoring music that was too sexual, but Serge Gainsbourg and Jane Birkin's 'Je t'aime ... moi non plus' somehow slipped through despite, you know, Birkin's orgasmic moaning.

Some other examples of censorship in Spain: the Rolling Stones' 1971 album Sticky Fingers was significantly edited for release in Spain. Firstly, the Spanish edition replaces 'Sister Morphine' with a Chuck Berry cover, 'Let It Rock', presumably because the blatant drug imagery in 'Sister Morphine' was too much for the Spanish censors. Secondly, the original Andy Warhol-designed cover with the zipper and the photo of tighty whiteys underneath was seen as too risque, and the Spanish edition has an alternative cover. Other censorship in Spain involved the Doors, Don McLean (the line about 'the father, son and Holy Ghost' referring to Buddy Holly et al was deemed offensive) and Ray Charles, while the text on the cover of the 1972 Some Time In New York City album by John & Yoko/Plastic Ono Band - a very left-wing record - was replaced with scribble (despite still having the provocative English title of a song on the record in big font: 'Woman Is The Nigger Of The World').

By 1977, the previous level of censorship of rock in Spain had effectively ended. The Spanish edition of Lou Reed's 1974 live album Rock'n'Roll Animal had removed the 10 minute live version of 'Heroin', replacing it with three shorter tracks ('Vicious', 'Can't Stand It' and 'Walk On The Wild Side'); by 1977, the album was reissued in Spain with 'Heroin' not only back in place on the record, but its presence prominently advertised on the cover of the record.