Question: For a normal 5 watt handy working in VHF or UHF freq with 50 ohm antenna , is it possible to use a same length coax cable instead of a stub antenna, so as to work like a crude antenna. Will this only result in extra capacitance/ VSWR damaging the system ?

Answer: 
You can remove the shielding of the coax leaving only the center conductor, but as mentioned in the comments the length will be off since this is way less then 1/4 wavelength and there is nothing added to increase the inductance. if the coax is 1/4 wavelength then it will work great.
youtube has a video of a piece of coax with the last 19" being separated between the center, pulling it out of the sheath. poor mans dipole. seemed to work
<http://bit.ly/2scIYD7>