Chrome adding extension with modified .crx file -

i trying add extension(ublock) modified preferences packaged install. able have chrome call extension through external_extensions.json

location (%programfiles(x86)\google\chrome\application\43.0.2357.132\default_apps\external_extensions.json )

with code

"epcnnfbjfcgphgdmggkamkmgojdagdnn" : {   "external_crx": "extension_0_9_5_0.crx",   "external_version": "0.9.5.0" } 

chrome loads extension can see calling form web store settings @ default. believe not calling file because have modified .crx file , getting errors(displayed below) when drag , drop extension chrome://extensions. not error if not modified .crx , use it's default settings.

crx_signature_verification_failed or crx_magic_number_invalid

i wondering there way correctly modify .crx file chrome accept or there better method install custom extension?

side note: have tried method of adding extension windows registry still have same problem pulling web store method start extension disabled. prefer method if can extension start enabled , contain settings want.

side note 2: reason doing way , not modifying extension through appdata\ because remote install, cannot have chrome run first time , create "profile" inside app data , extensions won't exist yet.