Can I get an earlier flight home from eastern Europe at any point during my vacation at no extra charge?

I am staying for 3 months and I'm kinda scared to make that commitment. If there is room on an earlier flight (say weeks earlier), wouldn't they let me change my flight date if I want to?

no

Depends on your flight company / booking agent. Where u fly to and from also. People like Easyjet let u for Free and some others do. But for a little premium you can buy flexi tickets from most carriers - this would be your best option from the beginning.

British Airways type of airlines will probably do, but that still depend on the type of the ticket, how long in advanced you got it etc. With cheap airlines you will have to pay the difference between the ticket you already have and the price of the one you'd like to get (check dates on the website). Good luck!

Home to....where? where is home??
Yes...they will allow you to change your flights. BUT depending on the type of tickets you bought (unrestricted vs. restricted) you might be looking at a huge cost difference. Even if it's an unrestricted ticket, the price might not be the same and if it's more, you'll have to pay the difference. If it's restricted, meaning, you bought it round trip, in advance, staying the weekend, non-refundable, etc. then you are bound by the terms of the ticket price and will be charged penalties and the difference in price. Call the airline and ask them what the restrictions on your ticket are, and explain them to you. Don't just do it, and hope...you'll regret it.