[PHB 240 (Find Familiar Spell Description)] You can’t have more than one familiar at a time. If you cast this spell while you already have a familiar, you instead cause it to adopt a new form. Choose one of the forms from the above list. Your familiar transforms into the chosen creature.
So, from what I understand of the familiar pact is that the spirit, with its memories, remains intact when I pocket-dimension my familiar, but I can perform the Find Familiar ritual to change its form, provided I used Find Familiar to create it.
This means that the Familiar is Unaligned? As a GOO-Chainlock, I would be able to make, say, a celestial imp that ISN'T trying to tempt me down the devil's path every minute. In fact, what shape it has gives it no bearing on its personality because it isn't the normal creature; it is merely a spirit given the form of an existing creature (for balance reasons).
For that matter, does what type I give it affect it? Celestials are generally good or lawful, fiends are generally evil, and fey are generally chaotic...but any creature with free will can technically be any alignment. (Do familiars have free wills? I know the PoC familiars are more cunning [PHB 108 'Your Pact Boon' box].)
I know some familiars aren't made via Find Familiar ([MM 69 (Variant: Imp Familiar)] states that an imp can form a contract with another creature, meaning a non-mage is a viable master), but the ones that are should be Unaligned because they don't exist until you cast the spell for the first time, and therefore have no experience or guidance towards any particular moral path.
I suppose if you do contract a natural imp, you can technically still pocket-dimension it and change its form if you are a mage with Find Familiar...
tl:dr; Big questions
(1) Do familiars have an alignment?
(2) Do familiars have free will?
(3) Can you change a form of a naturally formed and then contracted familiar if you have the ability to cast Find Familiar?
The real answer is whatever is most fun. But, IMO...
1: It reflects your own alignment.
2: No.
3: Any contract familiar is outside the spell. Possibly with it's own agenda.
tl:dr; Big questions
(1) Do familiars have an alignment?
To paraphrase the Rock: It doesn't matter what it's alignment is. It is your PC's flunky. Said PC has already made the deal (or had the deal made for them), so there isn't much (if any) need to corrupt the warlock. Of course an evil DM might put words into the familiar's mouth to advance the plot 
, but you can tell it to shut up or only speak when spoken to.
(2) Do familiars have free will?
In the abstract, yes (or at least as much as any outsider), but for practical purposes, no.
(3) Can you change a form of a naturally formed and then contracted familiar if you have the ability to cast Find Familiar?
[/quote] Not unless the contract specifies that, and then only because of the magic of the contract, not the find familiar spell.
mellored wrote:
lawrencehoy wrote:
[PHB 108 "Your Pact Boon" Box] Your familiar is more cunning than a typical familiar. Its default form can be a reflection of your patron, with sprites and pseudodragons tied to the Archfey and imps and quasits tied to the Fiend. Because the Great Old One’s nature is inscrutable, any familiar form is suitable for it.
It specifically says form. As in, can change. Only the fiendish ones can shapeshift; the sprite and dragon can't shapeshift, yet it's implied that the familiar is a form. They don't actually exist and are spirits given a body in the material plane.
After all, if you have an Unseelie patron, you're certainly not going to have a neutral good sprite or pseudodragon as your familiar, by your logic.
DKitten wrote:
cowleymen wrote: