modify-frame-parameters

modify-frame-parameters is a built-in function in `C source code'.

(modify-frame-parameters FRAME ALIST)

Modify the parameters of frame FRAME according to ALIST.
If FRAME is nil, it defaults to the selected frame.
ALIST is an alist of parameters to change and their new values.
Each element of ALIST has the form (PARM . VALUE), where PARM is a symbol.
The meaningful PARMs depend on the kind of frame.
Undefined PARMs are ignored, but stored in the frame's parameter list
so that `frame-parameters' will return them.

The value of frame parameter FOO can also be accessed
as a frame-local binding for the variable FOO, if you have
enabled such bindings for that variable with `make-variable-frame-local'.
Note that this functionality is obsolete as of Emacs 22.2, and its
use is not recommended. Explicitly check for a frame-parameter instead.