Section 6 of the Arms Act, 1959 prohibits which of the following acts without a licence?

As amended, s.6 requires a licence to "shorten the barrel of a firearm", to "convert an imitation firearm into a firearm" and to "convert from any category of firearms mentioned in the Arms Rules, 2016 into any other category". All three acts need the licence, while repair and testing for customers are dealings under s.5.