Since this was never answered, and I kept getting this thread as the first result when googling, I was able to solve this using these pieces of code:

xx_stage_id = fields.Many2one(comodel_name="xx.project.stage",string="Stage",tracking=True,index=True,default=_get_default_stage_id,group_expand="_read_group_stage_ids",    )
xx_stage_id_clickable = fields.Many2one(related="xx_stage_id", tracking=False)

@api.onchange("xx_stage_id_clickable")
def_set_stage_id_to_stage_id_clickable(self):
    for rec in self:
        rec.xx_stage_id = rec.xx_stage_id_clickable

For some reason having the same filed as clickable:1 in read mode and clickable:0 in edit mode did not seem to work, so I made this workaround which achieves the desired resuls.

Anyone??