Replacing an element of a list with another:
% lreplace {a b c d e} 1 1 foo
a foo c d e
Replacing two elements of a list with three:
% lreplace {a b c d e} 1 2 three more elements
a three more elements d e
Deleting the last element from a list in a variable:
% set var {a b c d e}
a b c d e
% set var [lreplace $var end end]
a b c d