When adding skills from the Character Sheet module, the stats can't be changed.
If instead of creating a new skill, you create a specialization of an existing skill, you get the same stats as that skill. You can use this if another skill in the same category has the desired stats (you would just need to rename the skill afterwards and you're done).
From what you ask, I guess you are more interested in adding skills to the standard skill list that is offered to all new characters.
That skill list, together with the stats for each, can be edited in the configuration files. There are a number of old posts about this in the
advanced customization thread.
I suggest you read what's mentioned there, and use that thread for any questions you might have about the customization of your skill list.
The same goes for the races. The free base package of ERA comes with just 2 races, and you can add more by purchasing additional packages on RPGNow. Since no ICE product currently on sale contains the MERP races, I can't publish them, so you would need to create them yourself.
This just means adding a new file in the
"Configuration/Races" directory, following the example of the common man and wood elf provided. If you need assistance with this, you can post them on the
advanced customization thread and we'll do our best to help.
About the adolescence skill ranks, I'm not sure if you are using RMC or RMFRP. In the case of RMC, adolescence ranks are not defined by race like it used to go for MERP, you would need to assign them manually once the character is created.
If you are using RMFRP, the concept of
culture will allow you to define fixed skill ranks at character creation, just like adolescence.
The Nomad culture will give you roughly the equivalent of a Rohirrim.
You could also create your own cultures by tinkering with the files in
"RMFRP/Configuration/Cultures" and
"RMFRP/Configuration/SubCultures".