I suspect that will do little good. They can just as well (and likely will) force you to register at some point under the threat of disconnecting your service.
Pre-paid SIM registration was introduced in Poland 7 years ago and existing cards which weren't in use were deactivated. Already active ones had a grace period after which owners either had to register these or pick new SIM and provide required personal data anyway. So I guess similar thing will happen for Lithuania.
The registration was available via short codes since operators in some cases already had the necessary personal data, or or it could be done by physically filling forms at operator's store.
That's how wirtualnemedia.pl portal described the purpose of SIM registration in its FAQ:
> What is the purpose of prepaid card registration? Does it function in other countries of the European Union?
> The primary purpose of the regulation is to increase the effectiveness of the Polish anti-terrorist system, thereby increasing the security of all Polish citizens. The obligation to register SIM cards is aimed at limiting the possibility of communication and camouflage for criminals, including those involved in terrorist activities. Some European Union countries have regulations imposing restrictions on the ability to purchase prepaid cards at service points of telecommunications operators. Such solutions are adopted in Germany, the UK, Spain, Bulgaria and Hungary, among others. The obligation to collect data on subscribers using telecommunications services is found in German law, among others.
It seems that now only Estonia and Latvia still will have "free" pre-paid SIM cards
