Sorry for the late reply, i barely have the time these days because of the exams, anyway you're trying to install the DLC without using ReactPsn but i don't think you can do that without the RAP file so here it is
1- Create a folder on the root of your ext HDD & name exdata
2- put the rap file you downloaded in the exdata folder
3- now create a new user profile & rename it to aa
4- install reactpsn via install pkg files
5- now enter your aa user profile & enter reactpsn(keep in mind you have to have your ext HDD plugged in the USB port closer to the BD drive)
now the ps3 will shut down & a messege will pop telling you the PS3 was shut improperly press x, now your aa profile will be renamed to reactpsn 11edat or something like that,you can rename it back to aa but don't delete it, you can delete reactpsn but don't delete aa user.
P.S Hahahaha, if this is an easy guide then i don't even wanna look at the normal or complicated one.. have a nice day.