Right now there is no way to get or set custom alpha channels from max script, but the next plugin version will contain two new functions maxwellGetCustomAlphaChan and maxwellSetCustomAlphaChan that will let you manipulate custom alpha channels on objects.
The function that sets the alpha channels does some internal validation so that you can't accidentally set a channel that doesn't exist, but due to this you can't set the custom alpha channels unless the active renderer is Maxwell.
Here is an example that assumes Channel0-Channel5 were created beforehand:
Code: Select allmaxwellGetCustomAlphaChan($Box001) - returns #(#Channel0, #Channel1, #Channel2)
nameArr = #(#Channel2, #Channel4, #Channel5, #Channel6)
maxwellSetCustomAlphaChan $Box001 nameArr
maxwellGetCustomAlphaChan($Box001) - returns #(#Channel2, #Channel4, #Channel5) because #Channel6 doesn't exist