Hi Jorge,
I don't think that it is technically possible to shift your assigned annual budget to overall level.
But do one try in testing system:
1) Create new WBS
2) Transfer your all actuals from old WBS to new ones wither via KB11N/CJ88.
3) But here commitment transfer is manual process, as we have to change manually account assignment elements in PRs/POs. There is no option for transferring commitments.
4) Assign pending works on new WBS and close/lock close ones.
Just give a try & check.
Also let others put their ideas on the matter.
Regards
Shishir