with las2las (or las2txt) you can only output one set of coordinate for every point. If you want both projected coordinated (e.g. x and y in a UTM projection) as well as geographic coordinates (i.e. x and y in longitude / latitude) then you will have to export twice and merge the CSV file somehow. The z coordinate does not get affected when changing the horizontal representation of the coordinates and will be identical. Of course you could in addition make a ellipsoid to geoid transform to get different z coordinates. For example, one way of doing that is using 'lasheight' with an external geoidal grid as the '-ground_points' and then running with '-replace_z'.
But let's assume the z coordinate stays the same for the example below using 'fusa.laz'. Then you need to do two things. First output the CSV file with the projected coordinates using 'las2txt' and the '-sep comma' option.
D:\LAStools\bin>las2txt -i ..\data\fusa.laz -parse txyzianrcupd -sep comma -o fusa.txt
D:\LAStools\bin>more fusa.txt
5880.963028,277999.97,6122342.20,64.35,10,89,2,1,5,145,1,0
5880.963032,277999.97,6122342.53,64.30,15,89,1,1,5,144,1,0
5880.978038,277999.52,6122339.74,63.09,12,89,2,1,1,132,1,0
5880.978043,277999.55,6122340.05,62.88,12,89,2,1,1,129,1,0
5880.978047,277999.53,6122340.41,63.00,18,89,1,1,1,131,1,0
And then do the (un-)projection to long/lat with 'las2las' before running 'las2txt' again and outputting only xy to a second text file:
Now you have to merge those two CSV files 'fusa.txt' and 'fusa_ll.txt' somehow ... (-: