You have posted in the packaging forum but it seems that you are asking from a food manufacturing perspective hence the requirements of BRC food are applicable? I can't seem to see if these liners are coloured, anyway, some relevant points:
5.1 PRODUCT DESIGN/DEVELOPMENT
5.1.2 All new products and changes to product formulation, packaging or methods of processing shall be formally approved by the HACCP team leader or authorised HACCP committee member. This shall ensure that hazards have been assessed and suitable controls, identified through the HACCP system, are implemented. This approval shall be granted before products are introduced into the factory environment.
There should be factory and transit trials
5.5 PRODUCT PACKAGING
5.5.1 When purchasing or specifying food contact packaging the supplier of packaging materials shall be made aware of any particular characteristics of the food (e.g. high fat content, pH or usage conditions such as microwaving) which may affect packaging suitability.
Certificates of conformity or other evidence shall be available for product packaging to confirm it complies with relevant food safety legislation and is suitable for its intended use.
Interpretation Compliance with legislative requirements
The company must be able to demonstrate that each item of product packaging meets legal requirements for its use (e.g. compliance with food contact regulations in the country of sale). This may be in the form of specifications, migration data or certificate of conformity. Where a declaration of conformity is used, any limitations on usage must be stated (e.g. the food types or storage conditions: ambient, chilled or frozen).
5.5.2 Product liners and bags purchased by the company for use in direct contact with ingredients, or work in process, shall be appropriately coloured and resistant to tearing to prevent accidental contamination.
Interpretation Product contact liners
Where companies are producing products for further processing, clear liners should not be used as they present a potential hazard for the next manufacturer.
You will also need to issue a new product specification and consider/gain Customer Approval
I've assumed that the supplier is already approved as per BRC requirements.