Can a Pact of the Chain Warlock have a celestial imp as a familiar?

Question

Pact of the Chain says (bold text mine):

You learn the find familiar spell and can cast it (...)

When you cast the spell, (...) choose one of the following special forms: imp, pseudodragon, quasit, sprite

The Find Familiar spell says:

You gain the service of (...) a spirit (...), the familiar has the statistics of the chosen form though it is a celestial, fiend or fey (your choice)

If you cast this spell while you have a familiar, you instead cause it to adopt a new form. (...) Your familiar transforms into the new creature.

Can a Pact of the Chain Warlock that has a celestial familiar cast the spell again and have assume the imp shape? Would it be considered a celestial?

Answer 1

Yes and yes.

It is all in the wording of the spell and feature.

it is a celestial, fiend or fey (your choice)

Implies that you have a familiar and pick what it is, regardless of its form.

If you cast this spell while you have a familiar, you instead cause it to adopt a new form.

Implies your familiar just changes form, but remains being what it is (e.g., Celestial).

choose one of the following special forms

Implies you have access to new forms.

So, yes, the familiar can take the imp shape, and it is still a celestial (assuming your previous familiar was one.