RE: Replacement for `aput' from obsolete assoc.el?

[Drew Adams]

> In an API, dunno exactly how emacs does this..., but setting
> several frame properties at once is a typical usage from XEmacs.
...
> (set-frame-properties FRAME PLIST)
> Change some properties of a frame.
> PLIST is a property list.

See GNU Emacs function `modify-frame-parameters'.
You pass it an alist, not a plist.

And an alist of frame parameters is what you get from function
`frame-parameters'.  

And an alist of frame parameters is the value of user options such as
`default-frame-alist'.

And yes, since Emacs uses alists for frame parameters you can take advantage (or
disadvantage) of shadowing frame-parameter values.