What certifications must one have to repair/alter propellers and instruments?

Question

According to 14 CFR 65 Subpart D

A certificated mechanic may perform or supervise the maintenance, preventive maintenance or alteration of an aircraft or appliance, or a part thereof, for which he is rated (but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments), and may perform additional duties in accordance with §§65.85, 65.87, and 65.95.

^{(Emphasis mine)}

What certifications are necessary to affect the repairs or alterations specifically excluded from a "mechanic" certificate?

Answer 1

I believe you need to be an FAA Certified Repair Station approved to work on instrumentation, propellors etc. as noted here

The FAA lists and approves ratings on a form called operations specifications. The operating specifications will also be displayed in the maintenance facility, usually right next to the certificate. Like other businesses, most maintenance facilities advertise on the Web and in trade magazines, so you have many ways to research what rating a particular repair station may have. There are basically six ratings that pertain to a repair station:

• Airframe

• Powerplant

• Propeller

• Radio

• Instrument

• Accessory

To be an approved Repair Station the employees must conform to

§ 145.157 Personnel authorized to approve an article for return to service.

(a) A certificated repair station located inside the United States must ensure each person authorized to approve an article for return to service under the repair station certificate and operations specifications is certificated under part 65. (b) A certificated repair station located outside the United States must ensure each person authorized to approve an article for return to service under the repair station certificate and operations specifications is—

(1) Trained in or has 18 months practical experience with the methods, techniques, practices, aids, equipment, and tools used to perform the maintenance, preventive maintenance, or alterations; and

(2) Thoroughly familiar with the applicable regulations in this chapter and proficient in the use of the various inspection methods, techniques, practices, aids, equipment, and tools appropriate for the work being performed and approved for return to service. (c) A certificated repair station must ensure each person authorized to approve an article for return to service understands, reads, and writes English.

They also must meet the requirements set fourth in:

(b) Meets the eligibility requirements of §65.101.

which you can find here.

You can find the full regulations pertinent to becoming a repair station here

Answer 2

Do some more reading at the link you provided in these paragraphs. I think that will answer your question.

§65.80 Certificated aviation maintenance technician school students.

§65.81 General privileges and limitations.

§65.83 Recent experience requirements.

§65.85 Airframe rating; additional privileges.

§65.87 Powerplant rating; additional privileges.

§65.89 Display of certificate.

§65.91 Inspection authorization.

§65.92 Inspection authorization: Duration.

§65.93 Inspection authorization: Renewal.

§65.95 Inspection authorization: Privileges and limitations.

A certificated mechanic with an airframe rating can approve and return to service an airframe, or any related part or appliance, of an aircraft with a special airworthiness certificate in the light-sport category after performing and inspecting a major repair or major alteration for products that are not produced under an FAA approval provided the work was performed in accordance with instructions developed by the manufacturer or a person acceptable to the FAA.

A certificated mechanic with a powerplant rating can approve and return to service a powerplant or propeller, or any related part or appliance, of an aircraft with a special airworthiness certificate in the light-sport category after performing and inspecting a major repair or major alteration for products that are not produced under an FAA approval, provided the work was performed in accordance with instructions developed by the manufacturer or a person acceptable to the FAA.

and further past the A&P ratings above is IA:

The holder of an inspection authorization may—

(1) Inspect and approve for return to service any aircraft or related part or appliance (except any aircraft maintained in accordance with a continuous airworthiness program under part 121 of this chapter) after a major repair or major alteration to it in accordance with part 43 [New] of this chapter, if the work was done in accordance with technical data approved by the Administrator; and

(2) Perform an annual, or perform or supervise a progressive inspection according to §§43.13 and 43.15 of this chapter.