Hello, for replace emmc Oppo F5, first of all, you have to backup NV partitions at first, including all necessery partition related to NV (nvram, nvdata, reserved 1+2+3+4, oppo_custom, and proinfo). This nv partitions is mandatory, or you will have touchscreen, camera , and IMEI problem that can't be repaired.
After have nv backup, you can proceed replacing emmc in this device by put new empty emmc to the board. But, before doing flashing procedure, there are some important step to make this device working properly.
1. Flashing using firmware version A.31
2. Uncheck preloader in first attemp of flashing.
3. Make Identify Device after first flashing, and insert the backup nv related(in above) partitions and do write
4. Flash preloader in last step.
5. Your device will fully working with IMEI and everybody happy
Hope this reply usefull and GooddLuck to All Of You.