The specialist engineers were drafted to work on the Edinburgh-North Berwick line to dislodge snow from a cutting near Drem.
The ScotRail Alliance with Network Rail said they worked through the night using floodlights and head torches to clear one of the last major remnants of last week’s “Beast from the East” snowfall.
About 200 cubic metres of packed snow overhanging the cutting were removed. Rail replacement buses ferried passengers between Drem and North Berwick.
The line was declared safe at 2:30pm yesterday after being checked by a “route proving” train.
The extended closure came after snowploughs managed to re-open the rest of the ScotRail network last weekend following heavy snow on Wednesday 28 February.
The four-mile branch line between Drem and North Berwick remained shut because of the threat of snow falling on trains over 100m of the cutting.
An Alliance spokesman said a snowplough had moved snow from the track on Sunday but the snow overhead posed a hazard because of rising temperatures.
He said: “Attempts were made to dislodge the blocks from above, but no attempts could be made to work from below due to the danger of being hit by the snow as it came down.
“The only safe option was to bring in specialist abseil teams to clear the snow and ice with hand tools as the site was too difficult to bring in any other kit.
“We had teams of six abseilers working continuously in shifts from 4pm on Thursday until midday on Friday, chipping the packed snow off the overhang into the cutting.
“A road-rail vehicle was then used to collect the snow blocks off the track and remove them.”
Other suggestions for clearing the snow have included explosives, which were used to break up avalanches from the West Highland Line at Tulloch, east of Fort William, in 2010, and mini water cannon.
Some passengers expressed frustration during the closure. Office worker @Tmckinnin tweeted: “Why still snow as snow should have melted by now?”
Andrew Mackie complained about poor co-ordination between the buses and trains. He tweeted on Tuesday: “I’m stuck at Drem station. Waited at North Berwick since 4pm and the bus was late and missed train. Stuck here until 5:35pm train and will miss start of important meeting. Four buses sitting at Drem.
“Surely you plan to link the coaches to the train. Really poor planning.”
However, East Lothian beauty therapist @Westgate39 wrote: “A thumbs up to the @scotrail on train guards for their patience and keeping us up to date with the Drem to North Berwick incident due to last week’s weather.”