Setting an asset below it's current build number is not recommended due to changes with features that were not available at the lower build. It works with simple things like buildings, for example, where there is nothing different, however, scripted assets such as interactive industries, locomotives, and other complex assets, will usually fail and cause other problem later on.
What the different build number references do is determine the compatibility of an asset within a build. The lower build numbers will mean the error-reporting is a bit more forgiving of certain errors that would be otherwise reported at a higher build number. The inverse, however, is down-versioning the build from a higher number to a lower one will mean that the newer features found in a higher build number will cause errors because these newer features were never available, therefore, are seen as errors.
Being a warning, a yellow ! and not a red !, you can ignore the message. These, as Shane says, are only warnings to let the script developer know that the asset needs updating. Updating should be considered because eventually warnings do become errors as we've found out recently with the transitions from TS12 to T:ANE, and with some assets going from T:ANE to TRS2019.