Place the following inside ~/.bashrc to have it run whenever you login.
xmodmap -e "keysym a = a A ae AE less less" xmodmap -e "keysym z = z Z guillemotleft less greater greater" xmodmap -e "keysym semicolon = period semicolon horizconnector multiply horizconnector multiply" xmodmap -e "keysym ugrave = percent percent percent percent percent percent"
The order of the letters after the = sign signify the modifiers to the keypress. The first is without modifier (natural key press of 'a'. Second is with Shift. Third and fourth is after a Mode_Switch (in RedHat Linux that is pressing Shift_R + Alt_R simultaneous, in that order) but without modifier after switching modes. And the last two is with Alt_R and Alt_R + Shift_R modifiers.
To see what currently is mapped use
xmodmap -pke | less