for f in ~/Desktop/*; do
    old=$(stat -f %B -t %s "$f")
    touch -t $(date -r $(($old - 1234567)) +%Y%m%d%H%M%S) "$f"
done

for f in ~/Desktop/*; do
    old=$(stat -f %B -t %s "$f")
    new=$(date -r $(($old + 1234567)) '+%m/%d/%Y %H:%M:%S')
    SetFile -d "$new" -m "$new" "$f"
done

ref_file=GOPR3440.MP4
new_time_for_that_file=0327160015 #date's format: 27th March 2015, 16:00

ref_file_timestamp=`stat -f %B -t %s "$ref_file"`
new_time_timestamp=`date -j $new_time_for_that_file +%s`
time_diff=$[$new_time_timestamp - $ref_file_timestamp]

for f in *; do
    old=$(stat -f %B -t %s "$f")
    new=$(date -r $(($old + $time_diff)) '+%m/%d/%Y %H:%M:%S')
    SetFile -d "$new" -m "$new" "$f"
done