Can you change an Eidolon's appearance?

[Senko]

May be a silly question but lets say you were going with the biped bodyguard Eidolon coulc you change the apperance of it or its armour e.g. Day 1 Its a 7' tall ogre wearing hide armour and then day 2 its a 5'6 human woman in a lamellar cuiriass and day 3 its a 6'2 figure in full plate or does it just have one specific apperance that doesn't change? Could you shift its apperance when changing its evolutions around while retaining the same general biped form?

Semi-related can an Eidolon's armour bonus be represented by it having a shield or other semi-seperate item or is it just armour/barding?

[Lady Asharah]

I don't see anything in the rules that specify either way, but they also say an Eidolon is an "aspect" of the creature you are summoning... so I guess as long as it's a different aspect of the same creature... why not?

[Darigaaz the Igniter]

I believe the eidolon's appearance is set whenever you adjust its evolutions. So, every time you gain a level or use the transmogrify spell (and a temporary change when using the evolution surge line of spells). The eidolon does have the share spell feature, so if the summoner gets access to any spells that would alter appearance they can use it on the eidolon that way. Alter Self being a 2nd level summoner spell comes to mind off the top of my head.