Entire word preprocessing

[hadibus]

I would like to transliterate between English and Anglo Saxon runes. The problem I'm running into is with the letter ᚦ (thorn), which corresponds to the sound "th" in "thistle"

Most of the time the "th <=> ᚦ" transliteration is good, but with some words ᛏᚻ would be more apropriate such as:

• apartheid
• fainthearted
• foothold
• knighthood
• knothole
• nighthawk
• penthouse
• warthog

Where the normal "th" pronunciation is ignored.

It would be nice if I could have code like this to have transliteration rules for specific words:

     pre_processor_mapping = {
       u"apartheid"   : u"aparᛏᚻeid",
       u"fainthearted": u"fainᛏᚻearted",
       u"foothold"    : u"fooᛏᚻold",
       u"knighthood"  : u"knighᛏᚻood",
       u"knothole"    : u"knoᛏᚻole",
       u"nighthawk"   : u"nighᛏᚻawk",
       u"penthouse"   : u"penᛏᚻouse",
       u"warthog"     : u"warᛏᚻog",
       u"th": u"ᚦ",
       u"sh": u"ᛇ",
       u"ng": u"ᛝ",
       u"st": u"ᛥ",
       u"qu": u"ᛢ",
       u"ea": u"ᛠ",
       u"io": u"ᛡ",
       u"æ":  u"ᚫ",
       u"œ":  u"ᛟ"
     }

This along with my mapping currently yields "warthog => ᚹᚪᚱᚦᚩᚷ" instead of "warthog => ᚹᚪᚱᛏᚻᚩᚷ".