I’m not quite what this thread has morphed into - but to get back to the OP - I’ve been in Marketing for many years and been involved with many commercial shoots.
@Voyager & @Taber are basically bang on.
Normally the process is that the company works with their ad agency to develop all the detailed ad content: location, script, costumes, tonality (funny, serious etc), as well as types of actors required to play the roles.
If the role is generic, i.e: “attractive 25-30 y/o black female” they are recruited from a local casting agency. We’d usually get a list of 20 or 30 actors that matched our criteria and select the one with thought was best. In that case the actor and their representative have no input into the ad. “Here’s the ad, it will take 1 day to shoot. Here’s what they’ll pay you. Do you want the role?”
On the day of the shoot, if the actor unilaterally decides not to do any part of the role (script, costume etc) they and their agency are fully responsible for all costs incurred as a result of their decision. This could include location, crew fees etc.
During the shoot itself, after they’ve completed the scripted ad, they may be given latitude by the director to do some variations for creative purposes, but that’s about it.
When using an “A-lister” like Matthew McConaughey, if he agreed to the proposed ad, he’d likely ask for and get a lot more creative input into the ad itself, both in advance and on the day of the shoot.
Obviously the actors level of input would vary depending on their star power and their advance contractual demands.
On the day of the shoot, if the company surprised him and asked him to wear a pink ballerina outfit that was not part of their agreed-to contract, he’d be within his rights to refuse but he’d still be obligated to do whatever he’d contractually agreed-to. If he walked off the set in a huff, he’d still be liable for any damages incurred as a result of him walking off.