I've just discovered the 'const' message function for the array - in which you can specify a single value to be written to an entire array.

Is there any way to use this function but only within a limited range of an array? For example, I would like to assign the value of 7 to index 5-26.

is this possible?

Not with one message. If you just need to write the same value to 11 indices, then an [until] loop will probably suffice. But if you need to set a constant to a large number of indices, you might find [iem_tab/tab_copy] useful. You can specify a specific range to copy with it, and for a very large number of indices it's noticeably faster than [until].