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No not at all. Virtually every rimfire rifle made today, and even some pistols, comes pre-drilled or dovetailed for scope mounting. In fact, if I were buying a rimfire rifle, one of the criteria guiding my choice would be the rifle's scope-mounting options. Once you have selected a scope, now you can find rings and bases to mount it to your rifle. Scopes do have different diameters, and you will need to choose rings of the proper size. You will also have to select the proper height. The larger the objective, the taller the rings will have to be to clear the barrel and/or sights.
Some prefer to leave the iron sights on, some like'em off. You can get rings that allow you to see through the scope mount and use the sights. Some designs make the scope too tall in this situation. They do make bases and rings that can be removed and remounted with minimal change to the zero of the rifle.