A1: There are several ways:
tail +2 < table2 >> table1
addrow < table | compute \
'if($0 ~ /^\t+$/) Column1="value1"; Column2="value2"; ...' \
> table.tmp
mv table.tmp table
row 'selection expression' < table > table.tmp
mv table.tmp table
A2: This is currently 'not in the cards.' NoSQL assumes that the tables are collections of variablelength records. Record level update requires fixed length records. It can be implemented by right padding the records with blanks to 'make room' for updates, but that is a bit of a kludge, IMHO. If you need such facilities you should use either /rdb or Starbase, or resort to a more usual SQL DBMS, either free or commercial. See also the workaround outlined in section Big tables.