as [Ignore] attribute's comment states - "When applied to the property of a model type, specifies that the property should be ignored" - and it did exactly what I needed - hid the property input field from the UI in admin panel.
However does that mean that this attribute will destroy property value of previously created pages with that property?
What I exactly want to do is to introduce new property on a page type and to use it instead of old one, but I can't remove old one, but want to hide it so admins wouldn't use it.
Episerver will not delete your data. You may safely add the [ignore]-attribute, or even completely remove the property definition from your code. As long as the property contains data, it will not be completely deleted.
You may also use:
"does that mean that this attribute will destroy property value of previously created pages"
No, [Ignore] attribute will not destroy previously saved property values. It will hide the Property.
Here is a good reference http://www.jondjones.com/learn-episerver-cms/episerver-developers-guide/episerver-properties/how-to-hide-a-property-in-episerver-cms-and-how-to-make-a-property-readonly