you can look on other topics on how to change what car it replaces i have done it many times for my ferrari's so they replace all the best cars on the game so there is not to much of them driving around it can be done u should just have to replace the car mods dat file so for e.g it was a alpha and u wanted it to be a banshee 
keep admiral the same and in readme it says car mods file  
admiral, nto_b_l, nto_b_s, nto_b_tw  
replace with banshee car mod dat and rename  
banshee, nto_b_l, nto_b_s, nto_b_tw and replace in banshee space NOT admiral  
and then handaling it should say something like this  
ADMIRAL      1650.0    3851.4   2.0    0.0 0.0 -0.05 75  0.65 0.90 0.51 	5 165.0 22.0 8.0  F P 	8.5   0.52 0 30.0  	1.0  0.15  0.0   0.27 -0.19 0.5  0.55		0.2  0.56 35000 	0			400000		0  1	0 
(but all in one Line)  
replace this in banshee slot and rename  
BANSHEE      1650.0    3851.4   2.0    0.0 0.0 -0.05 75  0.65 0.90 0.51 	5 165.0 22.0 8.0  F P 	8.5   0.52 0 30.0  	1.0  0.15  0.0   0.27 -0.19 0.5  0.55		0.2  0.56 35000 	0			400000		0  1	0 
and in car cols dat (replace with lines in readme)  
admiral, 34,34, 35,35, 37,37, 39,39, 41,41, 43,43, 45,45, 47,47 
replace in banshee slot and rename  
banshee, 34,34, 35,35, 37,37, 39,39, 41,41, 43,43, 45,45, 47,47 
and rename admiral.txd file and admiral.dff file what comes with the mod you got and  
rename banshee.txd and banshee.dff then extract banshee dff and txd in img tool 2.0  
and then delte them then add theese two then your redy to go  
If it goes well it should replace the banshee not admiral  
P.S this is only a example dont actuly use theese lines  
(this might reuin ure game but it is highly unlikely back up your files first! ) 
also i found a really detaild Fast And Furious Tokyo Drift Evo It Is Good Cause you Can Only Get The Paintjob Rims And Spoiler It you Tune it up !  
http://gta-worldmods.planet-multiplayer.de...;contentid=2580