You can use parameter forbidden_quality to forbid certain quality options. Just indicate names through a comma. Prohibited options will not be displayed in the menu, but may be available for the adaptive mode Auto of HLS or DASH (you can solve it by turning off the quality memory, adding Auto to the forbidden list and indicating the available quality option with the default_quality).
new Playerjs({
"id":"player",
"file":"[480p]//site.com/video.m3u8",
"forbidden_quality":"720p,1080p,Auto",
"default_quality":"480p"
});