Migration to new GL takes place considering the following into account.
Master Data: Existing Profit Centers will need to be assigned to segment.
FSG of GL accounts need to be revisited for new additional account assignments
(ii) Open items: SAP delivers transfer report, RGURECGFLEX to generate the new data
Open items tables (BSID, BSIK etc.)
Document Tables (BKPF,BSEG)
(iii) Opening Balances: Initial balance sheet items transferred to table FAGLFEXT via rollup from GLT0
EC-PCA and FI-SL ledgers if applicable are other starting points for migration of totals
(iv) Document Splitting: During data transfer documents are split based on configuration settings
Data transfer time frame should be wide enough to include all open items
Old documents cannot be split according to new account assignment, complete balance sheet according to new dimension is available after transitional time period
The material which you are refering is too huge and canot be shared in an email. Please let me know specifically what you want regarding migration and donot forget to assign points.