Is it common for a tracheotomy to be performed as a form of treatment for copd?

No. It is not a common treatment though it is used. It used usually in severe /end stage copd. These patient tend to have very severe COPD and need frequent treatment.
Copd. After about 10-14 days of a patient not being able to come off a ventilator, placement of a tracheostomy is considered. This could be for many diseases, including copd. Believe it or not, it is a more comfortable way to wean patients off of a ventilator. They do not need as much sedation, and they can, at times, speak.
Sometimes.... A tracheostomy can be done in the setting of COPD if the patient is on a mechanical ventilator and has trouble weaning off. A trach tube can allow this process to occur more comfortably. A trach tube can also help with secretion clearance by suctioning the airways especially in a pt with an impaired cough reflex. Impaired cough can be present in a COPD pt for a variety of reasons.
No. Tracheostomy only occurs when respiratory failure is present and no reasonable chance of removal from mechanical ventilation is present. Generally tracheostomy is a last resort to preserve life when lungs can't support themselves. It is not routinely recommended because it prolongs inevitable death.