《行行重行行》是产生于汉代的一首文人五言诗，是《古诗十九首》中的第一首，作者不详。
1: I don't think we should understand 申诉 as the word in its legal sense here. Maybe it's a combination of:
申明：state, express +
诉苦：grumble, complain, grievance
申诉现在之思念，: express present longing, repine the past
诗歌后十句写相思之意，
The last ten lines of the poem express yearning,
申诉现在之思念，
repine the past,
措辞前显，
the previous verses express
寓意深厚。
a profound meaning.
2: 申（明）足此意: amply express this idea.
“行行重行行”的意思是：走啊走啊走一直在不停的走。
It is easier to translate the poem in contemporary language:
你走啊走啊老是不停的走，
Keep going, keep going, never stop going,
就这样活生生分开了你我。
thus you and I in this life are parted.
从此你我之间相距千万里， (You know 千万里 just means "a great distance" ?)
Henceforth a million miles separate you and I,
我在天这头你就在天那头。
me in this corner of heaven, you in that corner of heaven.
The older text:(there are experts here who understand these old texts. I am not one of them!)
”行行重行行“ 言行之不止，
"Go on again go on" words and deeds endlessly,
致有“想去万余里”“个在天一涯”。(maybe should be: 各在天一涯）
cause (us to) "want to go more than 10000 miles" "each in their own bit of heaven".
三、四句表现极其遥远之概念，
these 3, 4 lines express the idea of great distance,
以申（明）足此意。
and amply express this idea.