Time signature differs from measure length

[Noeck]

Hi,

I want to write a piece with a alla-breve time signature but with four
half notes in a measure (4/2).

Is it better to overwrite the time signature stencil and use \time 4/2
(if yes, how?) or do it like this:

\version "2.18.2"

\relative c'' \scaleDurations 1/2 {
  \time 2/2
  r2 g g g | f f g b | b a b1
}

Cheers,
Joram