Hello,
I want to know, is there an option for asterisk to limit the addition of extensions? If there, How do it?
No, there is no such thing.
Also note that Asterisk uses “extension” in a specific sense, whereas many people use it to mean a telephone, and, in particular, a SIP endpoint, that directly represents a telephone. There is no hard limit to the number of SIP endpoints, and no distinction in that respect between those that represent telephones and those which represent other switches (pjsip.conf). There is no hard limit to the number of extension (extensions.conf, etc.)
Could you please explain where the question is coming from. This and other of your questions suggests you are thinking of Asterisk as though it were a closed source PABX, when it is actually an open source telephony applications toolkit.