I finally had some time to make this little macro for you. Change the field "MyField" into your own field. The macro splits your field into separate lines and counts them. Then an empty "newfield" is made. Every line is compared to the next line to see if the difference is "1". The current line is added to the variable "newfield" and if the difference is greater than "1", an empty line is added as well. Because the counter goes beyond the number of lines (counter+1) and this would result in an error, the macro checks this and terminates as soon as the end is reached. The last line is added to "newfield" without comparison (there's no next line to compare it with). The original content of the field is replaced by "newfield".
lines = split(fields("MyField"),CHR(10))
NumberofLines = 0
for each line in lines
NumberofLines = NumberofLines + 1
newfield = ""
for counter = 0 to NumberofLines-1
if counter+1 = NumberofLines then
newfield = newfield + lines(counter)
if lines(counter+1) - lines(counter) > 1 then
newfield = newfield & lines(counter) & CHR(10) & CHR(10)
newfield = newfield & lines(counter) & CHR(10)