Erik's answer is the best player-oriented practical solution - ask your DM, preferably one-on-one before or after a play session.
From a story & rules perspective, DMs are more likely to give an okay to changes that fit the following:
It shouldn't make you vastly more powerful. Most experienced DMs can spot a power-grab a mile away, and then there are the other players...
It shouldn't interfere much with other player's characters. Opportunities to flesh out your character shouldn't take away opportunities for your fellow players to shine. This is general advice - everyone is there to have fun, so share the spotlight.
It should make some kind of narrative sense - for the character, in the setting. In this case, your character didn't know what the object was, but you established that it exists, and just seems to be decorative. Something like suddenly becoming a vampire lord in a setting with no undead would be harder to swallow.
Don't expect to get everything you asked for, exactly the way you wanted. DMs have to balance out your request against the other players' needs, and the needs of the overall story/campaign. Also, sometimes the rules to implement what you're asking for are too complex for the table (or are of a much higher level than the characters).
In general, be flexible, accept any adjustments that your DM suggests from your original idea, and feel free to ask questions about how to introduce & integrate the new changes (one-on-one, not during group play).
Players are (or can be) as much a part of the game development process as DMs, and so long as both you & your DM are open-minded and take a little time to hash things out, your contributions can be a valuable part of making the game fun.