Just off the top of my head,
All proceedures are designed/approved by the state authority i.e. UK CAA. these procedures have published minimas wich must be equal to or above above the ICAO/state absaloute minimas.
The operator may further impose company minimas that are more restrictive that the published proceedures.
No airlines/airports/operators etc.. can design there own procedures. Jeppersen/Aerad etc just produce plates describing the published procedures - published in the UK AIP AD section (
www.ais.org.uk)
Companies may produce their own plates with their own minimas so long as it is approved (i.e depicts the published procedure)and is equally or more restrictive than the published minimas.
The criteria for proceedure design is described in PANS OPS.
Example - CAT 1 ILS Absaloute minimas DH 200ft RVR 550m
Specific aerodrome proceedure might reqire a DH of 500ft due local terrain (based on OCH's etc..)
A company may reqire that 20ft be added to all DH's
Result DH 520ft RVR 550
(Note further restrictions apply for single pilot operations)
Well thats how I interpret it anyway!
There are people out there who know alot more about it than me
Hope this helps.