Syncing on top of old chain ... works:
gsoil
INFO [05-12|15:42:48] Starting peer-to-peer node instance=Gsoil/v1.6.1-MMF-6ccff9a9/linux-amd64/go1.8
INFO [05-12|15:42:48] Allocated cache and file handles database=~/.soil/chaindata cache=128 handles=1024
WARN [05-12|15:42:49] Upgrading chain database to use sequential keys
WARN [05-12|15:42:49] Found genesis block without chain config
INFO [05-12|15:42:49] Initialised chain configuration config="{ChainID: 1337 Homestead: 0 EIP150: 0 EIP155: 0 EIP158: 0 Engine: ethash}"
INFO [05-12|15:42:49] Disk storage enabled for ethash caches dir=~/.soil/gsoil/ethash count=3
INFO [05-12|15:42:49] Disk storage enabled for ethash DAGs dir=~/.ethash count=2
INFO [05-12|15:42:49] Initialising Soil protocol versions="[63 62]" network=42
INFO [05-12|15:42:49] Loaded most recent local header number=2000267 hash=8b4f6b
2881fd td=32538335992977008
INFO [05-12|15:42:49] Loaded most recent local full block number=2000267 hash=8b4f6b
2881fd td=32538335992977008
INFO [05-12|15:42:49] Loaded most recent local fast block number=2000267 hash=8b4f6b
2881fd td=32538335992977008
WARN [05-12|15:42:49] Blockchain not empty, fast sync disabled
INFO [05-12|15:42:49] Starting P2P networking
INFO [05-12|15:42:51] RLPx listener up self=enode://46fce6fdc328596df97c8c2e4d1744b9bf5bfd540 ff8cf95e4880d797bd92e2cb52a81f38a9a49e51079f875c1adbdc2d4d6f503253e2d7188a494d421bd968b@[::]:30403
INFO [05-12|15:42:51] IPC endpoint opened: ~/.soil/gsoil.ipc
INFO [05-12|15:43:21] Block synchronisation started
INFO [05-12|15:43:25] Generating ethash verification cache epoch=66 percentage=29 elapsed=3.079s
INFO [05-12|15:43:28] Generating ethash verification cache epoch=66 percentage=79 elapsed=6.119s
INFO [05-12|15:43:29] Generated ethash verification cache epoch=66 elapsed=7.729s
INFO [05-12|15:43:30] Imported new chain segment blocks=5 txs=0 mgas=0.000 elapsed=7.933s mgasps=0.000 number=2000005 hash=39d755
b0b10d
INFO [05-12|15:43:32] Generating ethash verification cache epoch=67 percentage=19 elapsed=3.125s
INFO [05-12|15:43:36] Generating ethash verification cache epoch=67 percentage=29 elapsed=6.199s
INFO [05-12|15:43:38] Imported new chain segment blocks=179 txs=5 mgas=0.105 elapsed=8.100s mgasps=0.013 number=2000184 hash=e07fc0
ae2fa4
INFO [05-12|15:43:39] Generating ethash verification cache epoch=67 percentage=41 elapsed=9.274s
INFO [05-12|15:43:42] Generating ethash verification cache epoch=67 percentage=49 elapsed=12.640s
The interesting bit happens here:
WARN [05-12|15:43:42] Chain split detected number=2000000 hash=7b1028
4dbb4f drop=267 dropfrom=8b4f6b
2881fd add=244 addfrom=52e99f
68f5cdWARN [05-12|15:43:42] Chain split detected number=2000000 hash=7b1028
4dbb4f drop=267 dropfrom=8b4f6b
2881fd add=244 addfrom=52e99f
68f5cd
INFO [05-12|15:43:45] Generating ethash verification cache epoch=67 percentage=54 elapsed=15.725s
INFO [05-12|15:43:46] Imported new chain segment blocks=130 txs=0 mgas=0.000 elapsed=8.010s mgasps=0.000 number=2000314 hash=685315
68a11a
INFO [05-12|15:43:48] Generating ethash verification cache epoch=67 percentage=66 elapsed=18.894s
INFO [05-12|15:43:51] Generating ethash verification cache epoch=67 percentage=77 elapsed=21.919s
INFO [05-12|15:43:54] Imported new chain segment blocks=200 txs=0 mgas=0.000 elapsed=8.172s mgasps=0.000 number=2000514 hash=b76104
a2fa2e
INFO [05-12|15:43:54] Generating ethash verification cache epoch=67 percentage=90 elapsed=24.985s
INFO [05-12|15:43:57] Generated ethash verification cache epoch=67 elapsed=27.472s
INFO [05-12|15:44:02] Imported new chain segment blocks=248 txs=0 mgas=0.000 elapsed=8.036s mgasps=0.000 number=2000762 hash=6870f3
c0e3dd
INFO [05-12|15:44:10] Imported new chain segment blocks=198 txs=5 mgas=0.105 elapsed=8.029s mgasps=0.013 number=2000960 hash=875652
775d02
INFO [05-12|15:44:18] Imported new chain segment blocks=180 txs=0 mgas=0.000 elapsed=8.016s mgasps=0.000 number=2001140 hash=5b4646
254732
INFO [05-12|15:44:26] Imported new chain segment blocks=194 txs=0 mgas=0.000 elapsed=8.029s mgasps=0.000 number=2001334 hash=ffe879
be08d6
INFO [05-12|15:44:34] Imported new chain segment blocks=226 txs=7 mgas=0.147 elapsed=8.081s mgasps=0.018 number=2001560 hash=0c4cf1
49cebd
INFO [05-12|15:44:42] Imported new chain segment blocks=219 txs=0 mgas=0.000 elapsed=8.064s mgasps=0.000 number=2001779 hash=7448ae
de21e9
INFO [05-12|15:44:50] Imported new chain segment blocks=272 txs=6 mgas=0.126 elapsed=8.024s mgasps=0.016 number=2002051 hash=789e1e
7c3dc1
...
So ... looks like updating AFTER a new version has already passed the fork-block ... is unproblematic.