Which particular mods did you want to add to FTB Unleashed? Adding the whole pack isn't advisable for various reasons; but it's not impossible if that's really what you want to do. I'm playing unleashed with Galicticraft now so it's certainly possible.
Firstly what you need to do (not necessary but VERY helpful) is go into any unleashed world that works, hit E, go into "Options", then "block/item ID settings" and make sure "dump/ignore unused item (And the unused block id setting, too!) ids" is set to "dump", then click "Dump ID map now".
Find your FTB installation folder, it's usually where you first downloaded and opened the FTB launcher, and find the folder called "unleashed", in this folder click "minecraft" then open "ID map dump ~~~~". This shows you all your unused ids for config conflicts.
Next, where you found the "Unleashed" folder you should find a folder that relates to the lapito pack, open it, go into mods and find the mod name you want to copy. Copy these to a different folder called whatever you want. (I put mine on my desktop and remove it when I'm done). Next go back to the lapito pack -> minecraft folder and go into Config, find the folder/file for the mods you wanted to copy, and copy them to a *different folder* to your mods, to avoid confusion.
Lastly, Reopen the unleashed folder, and find the mod and config folders in here, too. Copy and paste the mod, followed by it's config, ONE AT A TIME. After adding each one, open the FTB unleashed pack via the launcher. If the game runs, great! Go into creative and test the mod was added, and all the items in that mod are actually that item because item ID conflicts don't crash your game.
However, if your game crashed, it's usually a block ID conflict, even if you can't work out what the crash report says. To fix this, we'll need the text file named "IDmap dump~~~" i got you to open earlier, at the top are unused block IDs, and at the bottom are unused item IDs.
Now, we go back to the config folder in the unleashed pack, and find the config of the mod we just added, open it with a simple text editor (notepad++ is your best bet, not sure if notepad works but try to avoid MS word) and find the item IDs (Depending on the mod, they'll be in different places.) and edit them so they are equal to block IDs on the unused list in your IDmap dump file.
If you get item conflicts, do the same with the item IDs, but use an empty item ID space to avoid bugs/crashes later.
100s of mods can be added to one pack like this! Feel free to message me if you're still not quite there- or post here, a lot of helpful people are experienced in adding mods to packs and adjusting their configs. Good luck~