Hello ahmed al ameen,
Authorized tech person was lied. Apple never customized WiFi module region wise. there are Global WiFi stands all manufactures should fallow such as WiFi a,b,g,n,ac (categorized by frequency band and cording mechanism) so your device support all bands,
if you have trouble as WiFi connection getting unstable you can simply download this software update given by apple inc
https://support.apple.com/en-us/HT203766
[guide|24759|Here] is the tear down guide and you can do the replacement your self
fallow step 15, 20, 21
if you still experiencing trouble with WiFi its better to use WiFi external dongle and it will cost below SLR.1000 and not required to teardown
Cheers!
Happy to help Sri lankan!