What are car seat manufacturers' recommendations for using -- or rather not using -- third party accessories with their car seats?

1. Infant Car Seat Manufacturer Statements on
Aftermarket Accessories
The following is a list of manufacturers' statements regarding the use of aftermarket
accessories such as seat covers, strap padding, insertable padding and attachable toys for
infant car seats.
Angel Guard:
Use only parts or accessories made by AngelGuard. Parts or accessories from other
manufacturers could alter the safety of the car bed.
Britax:
"The use of non-Britax Child Safety, Inc covers, inserts, toys, accessories, or tightening
devices is not approved by Britax. Their use could cause this restraint to fail Federal
Safety Standards or perform worse in a crash. Their use automatically voids the Britax
warranty." (This statement can be found under the Warranty section of all Britax Child
Restraint manuals)
Century:
"DO NOT use accessories or parts other than those provided by Century or Graco. Their
use could alter the function of the car seat." (This statement can be found under the
Warnings section of all Century Child Restraint manuals)
Car Seat Specialty (Car Seat Specialty, Nania, Safety
Baby):
"DO NOT use accessories or parts other than those provided by Car Seat Specialty, Inc.,
Safety Baby or Nania. Use of accessories or parts from other manufacturers could alter
the performance of the car seat." (This statement can be found under the Warnings
section of all Car Seat Specialty, Nania, and Safety Baby Child Restraint manuals)
Dorel Juvenile Group (Cosco, Eddie Bauer, Safety 1st):
"Dorel Juvenile Group does not recommend the use of any car seat accessories except
those recommended by the car seat manufacturer." (This statement can be found under
the General Warnings section of all Cosco, Eddie Bauer and Safety 1st Child Restraint
manuals)

2. Evenflo:
"DO NOT attach additional padding, toys, or other devices not made by Evenflo to the
child restraint. Items not tested with the child restraint could injure the child." (This
statement can be found under the Warnings section of all Evenflo Child Restraint
manuals)
We do not sanction the use of the Mighty Tite or any other similar device with our
products. (Statement by Randy Kiser, Director, Product Safety, Research &
Development, Evenflo Company, Inc.)
Graco:
"DO NOT use accessories or parts other than those provided by Graco. Their use could
alter the performance of the car seat." (This statement can be found under the Warnings
section of all Graco Child Restraint manuals)
Safeline:
"Do not use accessories or parts supplied by other manufacturers. These accessories or
parts could alter the function of the Sit 'n' Stroll and cause serious injury or death." (This
statement can be found under the General Warnings section of all Safeline Sit 'n' Stroll
Child Restraint manuals)