Hello. Yes it can be done but cost us $80 as we will need assisted reservations. This "manual" reservation override must be done by Lifemiles reps. This is the catch: It seems Lifemiles Desk in El Salvador has this override capacity while the Colombia and USA do not have such feature. Bear in mind that TACA (the Central American Carrier that was bought-up by Avianca) had a much better technologically superior tool than its now parent AVIANCA. (TACA mileage programme was called DISTANCIA).
So basically it seems that El Salvador has this edge to do the MANUAL reservation but not Colombia or USA. So if you call the US reservation office try to choose the Spanish agent-> then they route the call to El Salvador-> and as soon as they answer just speak English as they are Bilingual there. Hope it helps. (just completed one reservation 4 pax SJO-PTY-BOG-MAD-FRA-LHR in C Class for 55K miles each)