Sorry I can't reply to your comment. Thankyou for the answer! It is very helpful. I think i must have tried this before though.
The product template form is all messed up - default_code is in a different form inherit to the position i want it to go.
The Inherit id where i want the field to go is:
<field name="inherit_id" ref="product.product_template_form_view"/>
Whereas the field I want to move is in:
product.template.product.form
product.template
product.product_template_only_form_view
Error details:
Element '<field name="default_code">' cannot be located in parent view
I tried this and got no errors, but the internal reference is showing twice, and the second field (the new one) is blank
<record id="view_product_supplier_inherit" model="ir.ui.view">
<field name="name">product.template.supplier.form.inherit</field>
<field name="model">product.template</field>
<field name="priority">99</field>
<field name="inherit_id" ref="product.product_template_only_form_view"/>
<field name="arch" type="xml">
<field name="default_code" position="replace"/>
<label for="default_code" position="replace"/>
</field>
<field name="priority">99</field>
<field name="inherit_id" ref="product.product_template_form_view"/>
<field name="arch" type="xml">
<div name="options" position="inside">
<div>
<label for="default_code"/>
<field name="default_code"/>
</div>
</div>
</field>
</record>
:: EDIT ::
In response to your comment - yes I have tried that, and get 'not located in parent view' error. I have tried this:
<record id="view_product_template_form" model="ir.ui.view">
<field name="name">product.template.inherit</field>
<field name="model">product.template</field>
<field name="priority">99</field>
<field name="inherit_id" ref="product.product_template_form_view"/>
<field name="arch" type="xml">
<xpath expr="//page[@string='Information']" position="inside">
<label for="default_code" position="replace"/>
<field name="default_code" position="replace"/>
</xpath>
<div name="options" position="inside">
<div>
<label for="default_code"/>
<field name="default_code"/>
</div>
</div>
</field>
</record>
And the original still shows up, the duplicated field shows too though, which is a start, but unfortunately, neither stay updated when entering values (enter value, save, leave form, return to form, value not there).
Also - with the latest xml i posted (above) neither fields show a tooltip when developer mode is activated and the mouse is hovered over them.