old generation proton was possible to do it with minimal mods since all of that generation was exact copy from mitsubishi...so its just a matter or transplant the organ to the car..
but newer generation proton cannot since chasis was different...from mitsu (even it was similiar but surely not 100% fit like old generation proton
yes it can be done... but the question is, can it be done properly and legally??.. answer is no...
on legal issue... yes u will get stopped by JPJ officers if they finds out...
on technical issue... i dont think there are such expertise in malaysia which can do a good job in it... yes u can copy directly the design from another car (such as wira)... but can u make sure the welding job done is strong enough??... can u make sure the alignment of the suspension arms is not out??... in malaysia, many workshops do things pakai agak use eye see see only... 1 degree out of alignment ur car will drive like crab... handling will be worse den ur stock trailing arm...
not to mention, cutting and welding ur rear frame chassis requires alot of knowledge and experience in chassis tuning... weak struts mount can also result in bad handling...
my advice, change a better car is u really wanna look into good handling... civic eg/ek very good... satria neo also not bad...
if u wanna stick with ur saga, just do whatever mods available to improve the handling... coilover suspension... PU bush... front/rear weight distribution... better tyres... stabilizer bars, antiroll bars... etc....