This occurs under the influence of a preceding word. Lenition is not shown by any change in the spelling, however. Since these letter combinations were foreign to Latin, however, the writers of Old Irish apparently did not feel comfortable adopting them just yet. If you don't know how to make these distinctions, you can probably safely ignore them. Word Stress Old Irish, like most dialects of Modern Irish and Scottish Gaelic, had a strong stress accent on the first syllable of nouns, adjectives and the absolute forms of verbs.
Compound verbs are accented on the first syllable after the first preverb.
This is the restored text according to S amus Mac Math na, and my English. Below it are interlinear versions showing word for word translation and two styles of phonemic transcription.