Try this:

from odoo.models import BaseModel
basemodel_modified = BaseModel.modified

@api.multi
def modified_wrapper(self, fnames):
basemodel_modified(self, fnames)
self.env.context = dict(self.env.context, modifier_fnames=fnames, modifier_records=self)

BaseModel.modified = modified_wrapper

Now just look for modifier_names and modifier_records in env.context !

You could have a common method and control based on field triggered

 def main_method(self, field_triggered):
# Control with field_triggered field value
#     ....
    pass  

@api.onchange('field1')
def field1_trigger(self):
    self.main_method('field1')

@api.onchange('field2')
def field2_trigger(self):
    self.main_method('field2')