I guess your are not altering the model of the hilt: so you don't need directions to Gmax and all.
I believe what you might be looking for is a Hex editor.
What I use is named hexplorer or, well I got 2 such programs, XVI32.
I believe the last one can be found in the tools list in the tutorial section here at Holowan.
Should be at the top of the page: the tutorial section