I wonder what hack/configuration I should make to make these options available in User CP -> Options:
Set "Request A Read Receipt..."

Requesting a receipt when sending a private message is disabled by default. However, by checking the option below you can now enable "request a receipt" by default.
[checkbox] Yes, enable "Request a read receipt for this message".

Default Postbit

If you prefer the old-style postbit, using two vertical columns rather than the new horizontal layout, you can switch back by checking "Yes" below.
[checkbox] Yes, I prefer old-style postbit.

Thanks a lot.

Just create two custom profile fields.

The read receipt only needs a template edit.
The postbit needs a file edit though.

well the postbit part is easy also, and is only a template edit.

Just copy the postbit_legacy template and paste at top of postbit template

then add an if like

Make sure to change X to the number of the custom profile field.

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That's a more unorthidox way to do it.

Just remembered you could just add a plugin to global_start to change the postbit. If you create a field and tell me what field number it is I'll give you the code.

Hey, did you receive the PM? I have PMed you the field number and the details.
Thanks in advance.

Yeah, I'll do it either tomorrow night or at the weekend.

Any update?