I created ear file and i put it under Jboss-root\server\default\deploy now everytime i start the server it deploys it right?

Yes that's right. Your application will be deployed everytime you start the server.

is there any option to deply it only once and keep it deplyoed forever?

No. Whenever the server is shutdown, the application is undeployed. When you restart your server the application will be deployed again

 

in websphere for example the ear file is extrected in the file system and i've access to each file..

Check this out:

http://wiki.jboss.org/wiki/Wiki.jsp?page=ExplodedDeployment

what is the best way to change a jsp or properties file (in a deployed ear file) while the server is running?

Have a look at:

http://wiki.jboss.org/wiki/Wiki.jsp?page=RedeployAnApplicationWhenChangeAFileInAnExplodedDeploymentDirectory

If you are just changing a jsp page in a *extracted* war then you dont have to do anything. The changes will be picked up automatically. However, if the file is other than a jsp then you will have to follow the steps mentioned in the link above