Well, safety code issues aside ( it is technically illegal to modify ANY motors, including cutting off the cardboard casing to 'short' specs. ) ...

cutting down a 1/2A or A engine to 1.75" short, should pose no hazards, and would fly nicely.

However, you mention pouring out the ejection charge powder and using a regular engine for a booster - although it sounds liek this would still adequately ignite an upper stage engine - the DELAY would still be in place, and would therefor NOT stage at burnout, like a true booster engine would.

I would definately NOT reccomend using a delay engine as a booster, as staging delay would lead to tip-off and non-vertical flights.

~ AL

ps: and welcome to the forum, lots of rocket crazies here, me included, will help each other out as possible, guys teach me lots.