before going to discussion, i waht to clear some facts about indirect taxes.
indirect taxes are applied at source of taxation, where the assessee is liable for taxes at the point of manufacture and pay on clearance under excise,
right now service tax has also adopted same system to charge tax at the point of transaction of billing or receipt whichever is earlier.
under the provisions of excise there is no scope to amend / rectify the errors in return by assessee, ( no revise return permitted) any error in part of assessee means evasion only.
ACES is only receiving desk of documents and returns submitted, which are aligned with their internal server to put the same with commissionarate > division> range, where the appropriate officer inspects and do the needful.
till now no accounting software has direct access to indirect taxes, they can provide you snapshot of your transactions, but the assesee has to file returns as per the format and system provided by system of department through aces only.
you can develop the software / scheme for representation / calculation of records and tax liability, which can make the client easy with the accounting, but return filing is locked by ACES with their own custom made return filing utility.
at the point of filing the xml with server of indirect taxes, the server checks the authencity of program used, ( in developer section of excel utility the signature is locked by aces) and the columns / calculations are made as per laws / rules / sections of the department.
say if you select any notification no .it comes auto through a drop down menu, where the database is enclosed in a separate file annexed with the schema.
Do you think that ACES is non commercial entity or its part of CBEC? no its independent entity who have its own facilation centres, you can treat this at par with NSDL, where NDSL has no direct nexus with incometax, but handles all finance related transactions of incometax, for this they have internal renvenue arrangements with ministry of finance.
if you feel that you can develop anything better than the scheme provided by ACES, which will be more beneficial to clients, then get in touch with ACES or CBEC, offer your proposal, they will assess your proposal, on verification of your qualification and work experience in the field, and if viable they will make you familier with their system, authorize you to produce / develop softwares/ programs for their server.
Mere saying that I can develop something which is suitable for CBEC, does not authorize me to get access to the server, where millions of sensitive records are submitted by several clients, and indirect taxes has a major role in our GDP, any misuse / tempering of data will make a huge loss/burden to the govt, which is irrecoverable.
username / password is offered to clients to submit their own records / data/ return through ACES, and here the aces has two modules 1) web based where the assessee can fill the data online and submit, no need for additinal files 2) XML schema - where the assessee has to download the file utility , fill it, authorize it and then submit the same to the server, in the schema, if the file is tempered or altered, the server will refuse the file saying " filling error" as its treated "unauthorized access to server", coz the server recognizes that the alteration is done to misfeed the data to server, which will generate complication to assesse itself and if get associated with others then big mess in whole system.
use proper channels to get yourself registered with the department / ministry of finance to develop / produce products for use with the server, this will help you and department both, direct hit to the server without their authorization will lead some complication situation, where indirect taxes has brutal appearance for taxpayers.