Cleric that changes patron deity as alternative class mechanics

[Sir Edgen]

Hello everyone!
For a long time I had an idea about alternative domain mechanic for cleric - or similar class features for other classes. But before I explain myself, I would like to briefly tell how I understand details about gods and related terminology. I'll try me best to not to make your eyes bleed because of my crappy English.
So, that's how I see things: a mortal can WORSHIP any god he wants to, and not necessarily just one. He may aknowledge their powers and respect their gifts. Before the battle he will whisper prayers to, for example, Gorum, and during the hunt - to Erastil. However, mortals, and especially clerics, have only one PATRON deity, which reflects their beliefs and motives most closely and to whos realm the soul of mortal will go after death. So, if you are kind, honorable, if you protect weak and help people for no personal gain or sinister motives, your patron deity is most likely Iomedae - even if you don't consider yourself having any of these traits, don't aknowledge her power or even don't know about her existence. Correct me if I'm wrong.
My idea is the divine caster character, who CAN'T have a patron deity in a usual way. For example: NG cleric who gets divine spells because of extraordinary desire to help people or similar spiritual source (so in game language, instead of "worshiping" patron deity he gets his spells from connecton to ideas), but has only one domain - namely, Good - or no domains at all. He loves beauty, so he travels alot to see it, and understand that he wants to protect the peaceful world that he loves from evil monsters. The catch is, all these qualities remain in nearly absolute balance, so when his soul departs to Boneyard, Pharasma's buddies will never be able to understand to which of gods (Shelyn, Iomedae, Desna or Sarenrae) he is closer. One of the ways he gets domain powers and spells - when his party arrives to any settlement, he may find a temple of some good deity, that requests help. After a prayer, he becomes "an agent" of that deity during the requested mission and gets domain powers and spells specific to that god until he accomplishes the quest. The result will show, if the god pleased or not and will he or she allow him to use powers for an additional period of time or "spontaneously" invoke them in some situation that is important for that god (for example, when a priceless piece of art endangered cleric could swap domain to one of Shelyn's, but only for powers, not for spells).
The neutral variant could be the "madman" who considers himself as an upstart god, tries to choose his portfolio and helps different temples so he could gain those deities' support when his time to ascend will come.
I'm sure that mechanically this idea overpowers character and can threaten course of adventure, but can it be possible from RP point of view?
Thanks in advance!

[Spore]

I feel it should be handled like the Mongrel Mage Sorcerer, or the Martial Flexibility of the Brawler. Flexibility should come at a price imho. No steep price since Pathfinder honors specialisation more than general skill but a price nonetheless.

Other than that, I feel just a homebrew cleric variant would suffice. I'd go for a separatist-like cleric with two freely chooseable domains, which are the following:

Granted powers from the cleric’s domains function as if the cleric’s level, Wisdom, and Charisma were 2 lower than normal (minimum level 1) in terms of effect, DC, and uses per day. This also means the separatist doesn’t gain the domain’s higher-level ability until 2 levels later than normal. If the second domain grants additional class skills, the separatist gains these as normal.

Each day when he prepares spells, an idealist cleric can select different domains granted by deities available for his alignment to gain access to that domain’s spell list i

[Geddy2112]

Second separatist, as it can emulate a lot of what you are talking about. There is also the channeler of the unknow (https://www.d20pfsrd.com/classes/core-classes/cleric/archetypes/paizo-cleric-archetypes/channeler-of-the-unknown-ex-cleric-archetype/)n that works for ex/fallen clerics.

Cleric's don't have to have a deity. They can worship ideals or have a broader spirituality as said in the class description, or possibly worship a pantheon. "While the vast majority of clerics revere a specific deity, a small number dedicate themselves to a divine concept worthy of devotion—such as battle, death, justice, or knowledge—free of a deific abstraction. "

Also "Clerics meditate or pray for their spells"

Also "A cleric can select an alignment domain (Chaos, Evil, Good, or Law) only if her alignment matches that domain. If a cleric is not devoted to a particular deity, she still selects two domains to represent her spiritual inclinations and abilities (subject to GM approval). The restriction on alignment domains still applies."