As part of your contract with customers you may need to disclose changes to customer approved processes such as sanding and they may ask for supporting documentation that there has be no negative affect to their produce. I.e. Validation report
Validations can simply be a comparison between current method and new method with some form of measurement made such a comparison of sanding results to a surface finish standards or photographic compassion between hand work and machine work.
Formal reports should be written covering the following basics:
a) Description of the equipment (make, model, serial number) as appropriate
b) Author of the report
c) Report date
d) Purpose for performing the equipment validation
e) Equipment capabilities to be validated
f) Process capabilities to be validated
g) Calibration reports if required
h) Test, lab, inspection, first article reports as appropriate
i) Outcome/conclusion of validation performed
Report should contain sufficient data, pictures, drawing etc. that supports the conclusion of the report. Good place to start would be the new equipments specification sheet and any applicable industry and internal (procedure/work instructions) standards you currently must meet.
AS9100D requirements 8.1, 8.5.1, 8.5.1.2 and 8.5.6 are applicable to equipment and process validation. Software programs referenced in 8.5.1.1 would be validated during equipment/process validation and as the standard requires, must be completed prior it use in producing product intended for delivery to the customer.
The short answer to your question would be yes you should perform a validation to assure yourself and your customers that the new method works and produces results similar (or better) than current method.