So the question indeed becomes what should be regarded as a "Bitcoin" unit? At the moment it is 100,000,000 Satoshis. I say that this framing is not very convenient to the ordinary members of the human species whose grammar (in many different languages) and psychology over the centuries has been developed in such a way that they prefer to talk in integers when it comes to money. the most that those primitive species called *humans* who are not programmers, hackers, geeks and mathematicians have grown accustomed to think of the money is no more than 2 decimal places. There's a problem of acceptance and adaptability there. There are in fact many perception related problems there, which are outlined in the article that I linked to above. When Bitcoin was $1 or $10 this problem was not so obvious, but as Bitcoin increases in value this problem is becoming worse and worse. So something needs to be done to revalue what we call "Bitcoin", so that instead of 100,000,000 satoshis it becomes 100,000 satoshis.
You clearly haven't thought through how you would enforce your bitcoin re-valuation in a peer-to-peer decentralized system.
There is no authority that can declare that a bitcoin represents a particular number of Satoshi. Each user is allowed to rename any number of base units in any way that they like. There is no law or authority that can stop them. They can even release modified wallets that use their new naming system.
If you want the naming system changed, create a wallet that changes it (or pay a programmer to do it for you). Then release it to the public. Those that agree with your system will use it. Those that don't, wont.
However, you'll most likely find that you are fighting against a very strong network effect. There is a significant majority of the users and people who are aware of bitcoin that expect 1 BITCOIN to represent a particular thing. If you try to change that, you will cause enough confusion between those that want to leave it the way that it is, and those that want to change it, that eventually one party will give up and adopt the naming convention of the other.
Since there are already names that allow us to use integers to talk about smaller quantities, you may find it difficult to convince enough people to use your system.
Note, the base integer unit in the blockchain is the Satoshi (equivalent to 10 nBTC). If we think of this like we might the US penny, then saying something costs "3 bitcoin" is just a nickname for a large quantity of Satoshi (in the same way that saying something costs "3 grand" might be a nickname for a large quantity of pennies). Do we "redefine" how many pennies "a grand" is so that we don't have to say that a hamburger costs 0.005 grand? No. We simply use a different nickname. Perhaps that burger costs "a fiver", or "a lincoln", or even "5 bucks".
Humans have been creating nicknames for various quantities of money to avoid excessive zeroes and decimals for as long as they've had money. This won't change with bitcoin. 1 BTC will almost certainly always be the same amount of Satoshi as it is today, but eventually people will gravitate to nicknames for smaller quantities of Satoshi.
Perhaps a mBTC (milliBitcoin) will be called a MilliBit, or a Millie, or a Mill, or an emBee, or an emBit. The nicknames will form organically as the need arises. Feel free to use whatever nickname you like best. Either others will like your choice and will adopt it as well, or they won't and eventually you'll switch to what ever seems to be in common use.