kmacro-execute-before-append

kmacro-execute-before-append is a variable defined in `kmacro.el'.
Its value is

t

Documentation:
Controls whether appending to a macro starts by executing the macro.
If non-nil, using a single C-u prefix executes the macro
before appending, while more than one C-u prefix does not
execute the macro.
Otherwise, a single C-u prefix does not execute the
macro, while more than one C-u prefix causes the
macro to be executed before appending to it.

You can customize this variable.