Welcome, Bapinurnose!
Yes, they can.
Are they any difference between LHTR and OOB rules ?
A lot of differences.
Mainly the LHTR are more clear, resolve some problems of the rules (for example the deployment of fighters on AC) and form a more rational set of rules.
What I can recall right now are the following points:
Clarification of the SBR and rocket attacks rules;
Introduction of the 9 city victory (Marginal Victory that is IMHO the more useful for face to face game);
Correction of the deployment rule of fighters on the AC.
Availability of Weapon development in the deplyment phase.
Correction of the National Advantages.
A good think to do is to read the thread that discuss of the LHTR rule. NAturally the best thing is download and use them!
See this thread for an in-depth discussion of the differences between the two rule sets.
where can you download the LHTR from?
Right here.