On other hand, will this be possible to compile the source code for 1.0.1n to work with existing version of Apache 2.4.12 x64?
It's possible sure, 1.0.1o now. Here's the problem. We should have already been using 2.4.13 with 1.0.1n but someone vetoed the release to get in a fix for a CVE. The fix was added and 2.4.14 was tagged but the CVE caused a bug. That's been fixed. There is one other issue on the table to being discussed and 2.4.15 will be tagged.
It's a lot of work making all the updates, do we want to do it only to have it be superseded in a few days. Not only that but OpenSSL 1.0.2c, 1.0.1n and 0.9.8zg was released on 11-Jun-2015. I spent most of the day compiling these for all the Apache version (2.4, 2.2, x86 & x64). Then on 12-Jun-2015, 1.0.1o and 1.0.2c were released. So 2/3 of all that time spent was wasted between OpenSSL and ASF.
I assume you are talking of the logjam, a proper ssl configuration and DH Prime > 1024 bit is not vulnerable to logjam even with 1.0.1m as far as I know. 1024 bit DH prime has been a discouraged for over a year now.
Short answer. No. I have to take my mother to a doctor appointment tomorrow in the AM and I have one in the afternoon. I'm hoping 2.4.15 will be tagged tomorrow and I can start working on that in the evening.
It's 9:25pm June 15 here, the tomorrow I speak of is June 16 here.