lreplace

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