A process for the preparation and modification of additives, with a zeolite base and a high silica alumina ratio (SAR) like the ZSM-5, to increase the yield of propene and LPG in low severity FCC operations, that seeks to maximize the production of medium-distillates with low aromaticity and to minimize molecular cracking in the LCO range. The additives involved guarantee an increase in light olefin yields without altering the yield or the quality of the LCO produced. The innovative process includes surprising actions from rare earths (RE) on the active sites of zeolite, that at once partially block their pores and, in this way, make molecular cracking in the medium-distillate range difficult, which preferably occur at low reaction temperatures and keeps the remaining sites quite active. These sites are sufficiently active to crack smaller molecules in the gasoline range, guaranteeing an overall increase in light olefins and allowing the additive involved to be used industrially in operations to maximize medium-distillates in an FCC unit. This new additive may be obtained by modifying any commercial ZSM-5 zeolite additive.