Use the submatrix() function, possibly together with the stack() function.
Or do you mean to change their values instead of their position?
I would like to change the values of the last third or so, by a tiny bit.
I suppose I could maybe use the submatrix and stack to: disassemble, manipulate and reassemble.
Or is there an easier way?
if you wan to change the value of a vecor v, lets say at position 123, you can simply write v[123:=<any value you want>.
Or if you want it to increase by 1% you may write v[123:=1.01*v[123.
The "[" is the keyboard short for the vector index.