impact of subledger accounting in R12 on upgrade from 11.5.10.2 to R12

 Hi Folks 

 I am a Oracle apps dba trying to understand the impact of subledger accounting on the upgrade. 

About the system : We have a 2 node 11.5.10.2 instance on linux box 3 (32 bit) that we have to move to R12 (on 64 bit as 32 bit is not an option as per the certification matrix ). the target os is Linux 6 

I did go through the manuals but am not clear of the impact. 

My concern is that our customizations that were written for 11.5.10.2 should not break because of subledger accounting. (may be i am getting paranoid here) . or will it (if yes then why ? )